Hello, Codeforces!

Imakf and I are glad to invite you to Codeforces Round #808 (Div. 1) and Codeforces Round #808 (Div. 2), which will take place on Jul/16/2022 17:35 (Moscow time). In both divisions, you will be given 6 problems and 2 hours to solve them all.

We would like to thank:

• Monogon for his 1-year cute coordination and very helpful discussion.
• KAN for the great help with round preparation.
• Wolam for his discussing the problems with us, which helps us to find the solution.
• smg23333 for donating his csgo time to test the problems in advance.
• AliShahali1382, SecondThread, wxhtzdy, taran_1407, Retired_cherry, antontrygubO_o, Tlatoani, errorgorn, hg333, kassutta, timreizin, Taday, Qiulyqwq, dorijanlendvaj, arvindr9, gamegame, EmptySoulist, prabowo, Yakumo_Ran, star_xingchen_c, generic_placeholder_name, 74TrAkToR and Ari for testing the round and their invaluable feedbacks.
• MikeMirzayanov for amazing platform Codeforces and Polygon.
• geranazavr555, KAN, myav and unreal.eugene for translating the statements into Russian.

Score distribution will be announced before the round.

Wish you all wouldn't gain negative ratings in this round! (This is theoretically possible XD)

UPD1: Score distribution is

Div 2: $$$500 - 1000 - 1500 - 1750 - 2250 - 3000$$$

Div 1: $$$500 - 750 - 1250 - 1750 - 2500 - 3250$$$

UPD2: Editorial

UPD3: Congratulations to the winners!

Div 1

1. Isonan
2. djq_cpp
3. tourist
4. jiangly
5. Um_nik

Div. 2

1. _WidowMaker_
2. N193r
3. Ayaka_s_Dog
4. PaiGuChicken
5. NothingOccurred

Hello Codeforces,

We are glad to invite you to Codeforces Round 807 (Div. 2), which will be held on Jul/15/2022 16:35 (Moscow time). As usual, the round will be rated for participants with ratings lower than 2100, while those who have higher ratings are encouraged to participate unofficially. Please note the unusual start time.

You will be given 6 problems to be solved in 2 hours and 15 minutes. There may or may not be interactive problems, so you are encouraged to prepare in case they do appear by reading this guide.

The round is authored by abc241 and me, while joining us is also inwbearX who contributed significantly to the preparation. This is our first time setting rounds in Codeforces, and it wouldn't be possible if there were no support from the following people.

• errorgorn for fantastic coordination.
• KAN, mtw, geranazavr555, unreal.eugene and MikeMirzayanov for translating the statements into Russian.
• antontrygubO_o, kevinxiehk, mango_lassi, Adam_GS, mtw, Utkarsh.25dec, yz_, thanhchauns2, TLP.39, 36champ, jampm, DeMen100ns, Neothehero, and somerandomaltacc3034 for testing the round.
• MikeMirzayanov for Polygon and Codeforces.

The score distribution is $$$500$$$ — $$$1000$$$ — $$$1250$$$ — $$$1750$$$ — $$$2500$$$ — $$$3000$$$.

We are looking forward to your participation. Good luck and enjoy our round!

Update: the editorial is up!

Update 2: Winners!

Div. 2

1. stemroot
2. UtopianZ
3. WYZFL
4. H_stove
5. myeeye

Div. 1 + Div. 2

1. tourist
2. SSRS_
3. stemroot
4. Um_nik
5. arvindf232

Hello Codeforces!

SlavicG, flamestorm, MikeMirzayanov and I want to invite you to Codeforces Round 806 (Div. 4).

It starts on Jul/12/2022 17:35 (Moscow time).

The format of the event will be identical to Div. 3 rounds:

• 5-8 tasks;
• ICPC rules with a penalty of 10 minutes for an incorrect submission;
• 12-hour phase of open hacks after the end of the round (hacks do not give additional points)
• after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated
• by default, only "trusted" participants are shown in the results table (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer).

We urge participants whose rating is 1400+ not to register new accounts for the purpose of narcissism but to take part unofficially. Please do not spoil the contest for the official participants.

Only trusted participants of the fourth division will be included in the official standings table. This is a forced measure for combating unsporting behavior. To qualify as a trusted participant of the fourth division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them),
• do not have a point of 1400 or higher in the rating.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400 (or you are a newcomer/unrated), then the round will be rated for you.

Many thanks to the testers: TimDee, Gheal, Max_Calincu, qwexd, _Vanilla_,sandry24, jampm, haochenkang, tibinyte, Etherite.

We suggest reading all of the problems and hope you will find them interesting!

Good Luck!

Update: Editorial

Hello! Codeforces Round 805 (Div. 3) will start at Jul/10/2022 17:35 (Moscow time). You will be offered 7-8 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a rating of 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks.

You will be given 7-8 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of our work. Problems have been created and written by ITMO University teams: MikeMirzayanov, MisterGu, myav, Vladosiya, Aris, senjougaharin and me Gol_D.

Also many thanks to turmax, ivanz, antonis.white, Ronnie007, okwedook, oversolver, Kavaliro, antoshkin, omikad, yorky, Jostic11, Ziware, Kniaz, andrey.starodubtsev, Spaggetti and aniervs for testing the contest and valuable feedback.

Good luck!

UPD: Editorial

Hello Codeforces!

On Jul/08/2022 17:35 (Moscow time) Educational Codeforces Round 131 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 or 7 problems and 2 hours to solve them.

The problems were invented and prepared by Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Our friends at Harbour.Space also have a message for you:

Hey, Codeforces!

Welcome to the 131st educational round hosted by Harbour.Space and Codeforces.

Quite exciting, isn’t it? Now it's time for you to dive deeper into the competitive programming world with the 10 days intensive Summer Camp organized by Harbour.Space and Leagues of Code.

Don’t forget about the discounts for participating in our Summer Camp. Every member of the Codeforces community gets a 30% discount for on-site participation or a 50% discount for online participation with promo-code CFLOC2022.

Our Summer Camp is a training program that will teach participants competitive programming. It will take place in Barcelona and online on July 18-29, both participation formats are available.

We are inviting students ages 10 to 24, interested in improving their skills or seeking intensive, high-level training prior to the IOI. Teachers in the camp will be ICPC World Final Silver medalist 244mhq, SWERC 2022 Winners MaksymOboznyi, ICPC World Final Champion pashka and others. Participants will be divided into classes based on their level and previous experience. Classes will be held in English.

Good luck with the round!

UPD: Editorial is out

Hello, Codeforces.

We have exciting news! Look at the logo. See the changes?

Yes, we are happy to announce our new sponsor and partner – the TON Foundation!

We appreciate their support!

The Open Network (TON) is a fully decentralized layer-1 blockchain designed by Telegram to onboard billions of users. The TON Foundation is aimed to further develop and advance the TON Blockchain and its related products for a mass audience.

Andrew Rogozov, founding member at the TON Foundation, says, "We strongly believe in the idea of competitive programming itself, because it is in the TON Blockchain DNA." The TON Blockchain protocol was designed by Nikolai Durov — who is a two-time ICPC world champion, a three-time IMO gold medalist, a multiple IOI medalist, and a co-founder of Telegram — and other winners of international competitions. Now the TON Blockchain core team consists of winners of blockchain contests held by Telegram.

The TON Foundation has already supported the CodeTON Round 1 earlier in March 2022. More than 22K users were registered, and 12K participants made at least one submission. "Codeforces is an unparalleled platform for developing the programming skills of coders all over the world. We are of one mind with the Codeforces team that such contests reveal a treasury full of talents," adds Andrew Rogozov.

I send rays of gratitude to Telegram and personally to Pavel Durov, who has supported our community for many years. With this help we have come a long way — we have run hundreds of rounds, developed the ecosystem, our community has grown hundreds of times. And we are moving forward! Support from the TON Foundation pleases with its succession.

I'm happy to announce that starting July 2022, we have the option to increase problem writer payouts. Hooray!

• Div. 2: $300;
• Div.1 + Div. 2: $600;
• sponsored round: $900.

In addition, we continue to encourage payments in cryptocurrency. In this case, we pay out +25%. I look forward to new rounds on our platform.

— Mike Mirzayanov

Hello, Codeforces! Or, as we like to say in Romania: Noi nu spunem asa ceva, Codeforces!

We are proud to finally invite you to participate in Codeforces Round #804, which will start on Monday, July 4th, 2022, 14:35 UTC You will be given 5 problems and 2 hours to solve them. We greatly recommend to read all the problems, statements are very short and straight to the point.

In this round, the theme is not Independance Day related. I know, maybe we should've made the theme "Freedom", but we are not Americans and the puns within the problems were already written.

Joining me on the problem setting panel are:

• Setters: Gheorghies Gheal Alexandru, Cozma tibinyte Tiberiu-Stefan, Voicu valeriu Mihai Valeriu

• Vip-Testers: Um_nik, antontrygubO_o, BlueDiamond, lucaperju, atodo

• Testers: LucaIlie, borgar02, freak93, $$$\,\,\,\,$$$ Ionut_Padurariu, Lemur95, FairyWinx, $$$\,\,\,\,$$$ Brodicico, apostoldaniel854, Kirill22, $$$\,\,\,\,$$$ Olympia, lavish315, Kuroni, $$$\,\,\,\,$$$ caheman, theodor.moroianu, TheScrasse, $$$\,\,\,\,$$$ 244mhq, VladHaivas0205, Tudy006, stefdasca, CaesarPP, Fanurie, elizatoma000w, mat50013, IacobTudor, codrincrismariu, Matteo.Verz, mircea_007, amcbn, mihneacazan, armand09

• Coordinator: Artyom123

Also, we would like to thank:

• intrusiv for not deserving to be publicly named
• tibinyte for being a "codechef carry".
• Gheal for getting order #804 at KFC.
• lucaperju and VladHaivas0205 for inviting some of the testers :)
• Artyom123 for captivating coordination, rejecting only Boring tasks. 9 div2Bs to be precise
• antontrygubO_o for improving one of the tasks!
• TON for supporting this round, details can be found in this post.
• MikeMirzayanov for great platforms, Codeforces and Polygon!

Here is the scoring distribution: $$$500 - 1000 - 1500 - 1750 - 2500$$$.

Good luck & have fun & the third part!

UPD1: Editorial is up!

UPD2: Winners!

Div 2:

• First_Brave_Niuniu
• fAKelyh
• ifzw
• H_stove
• Remakee

Div 1:

• SSRS_
• heno239
• jiangly
• disorientation
• noimi

Hi Codeforces!

ScarletS and I are glad to invite you to Codeforces Round 803 (Div. 2) which will be held on 28.06.2022 17:35 (Московское время). The round will be rated for participants with rating lower than 2100. The theme of the round will be déjà vu! (Wait, wasn't that already a theme before?)

Thanks to the people who made this round possible:

• errorgorn, for his fantastic coordination of the round;
• MikeMirzayanov, for creating the amazing Codeforces and Polygon platforms;
• KAN, for translation of the statements into Russian;
• antontrygubO_o, AmShZ, Ari, MagentaCobra, AlperenT, satyam343, Vladithur, phattd, fishy15, tenth, Surprise_Me, jampm, Yangster, Il9, ak2006, FionnKimberOShea, Codula, and bakekaga for testing the round, catching any mistakes and providing lots of valuable feedback!

Thanks to NEAR for supporting this round, details can be found in this post.

You will have 135 minutes to work on (and solve!) 7 problems. At most one of the problems will be interactive. Make sure to read this blog and familiarize yourself with these types of problems before the round!

The scoring distribution is $$$250-500-1000-1500-2000-2500-3250$$$.

Good luck, and see you on the scoreboard!

UPD: Editorial is out!

Hello Codeforces!

On Jun/25/2022 17:35 (Moscow time) we will hold Codeforces Global Round 21.

It is the third round of a 2022 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The prizes for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2022:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2022 supported the global rounds initiative!

All problems except one are authored and prepared by me. The other problem is authored by gyh20.

We would also like to thank the following people:

• irkstepanov for coordination, and KAN for helping as well.
• gyh20, ShuiLaoshi, ilyakrasnovv, fengzhengwei, Vladithur, antontrygubO_o, Golovanov399, snowysecret, ak2006 for testing.
• MikeMirzayanov for polygon and codeforces.

Round information:

• duration: 2 hours and 15 minutes
• number of problems: 8
• score distribution: 500-1000-1500-2000-2000-2500-3250-4000

We are looking forward to your participation!

Upd Editorial https://codeforces.net/blog/entry/103479

Upd Winners!

1. ksun48
2. jiangly
3. Um_nik
4. Petr
5. maroonrk

Hi!

This Sunday will take place All-Russian olympiad for students of 5-8 grades, in the name of Keldysh. Good luck to all the participants! Olympiad is conducted under the guidance of the Moscow Olympiad Scientific Committee, in particular GlebsHP, ch_egor, Endagorion, vintage_Vlad_Makeev, Zlobober, meshanya, cdkrot, voidmax, grphil, fedoseev.timofey and, of course, Helen Andreeva.

We are happy to announce the Codeforces Round #802 based on the problems of this olympiad! It will be a Div. 2 round, which will take place at Jun/19/2022 12:05 (Moscow time). You might have already participated in rounds based on the school olympiads, prepared by Moscow Olympiad Scientific Committee (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567, 583, 594, 622, 626, 657, 680, 704, 707, 727, 751, 775). Please notice the unusual time.

The problems of this olympiad were prepared by Siberian, _overrated_, Igorbunov, Ziware, talant, Olerinskiy under the supervision of fedoseev.timofey.

Thanks to 74TrAkToR for their help in organizing the Codeforces version of this contest and one of the problems, MikeMirzayanov for the Codeforces and Polygon.

Also I would like to thank the Tinkoff company and personally Tatyana TKolinkova Kolinkova for great help with organizing the competition.

Thanks to NEAR for supporting this round, details can be found in this post.

Good luck!

UPD1: Thanks to Um_nik, 244mhq, MichsSS, zarubin, TeaTime, devid, Mangooste for testing.

UPD2: Scoring distribution: 500 — 1000 — 1500 — 1750 — 2500 — 3000

UPD3: Winners!

Div. 2:

1. teacherone
2. zsxdcfv
3. AndrescuIII
4. rhzmydd
5. Yuki991

Div. 1 + Div. 2:

1. SSRS_
2. noimi
3. Fysty
4. peti1234
5. teacherone

UPD4: Editorial