Welcome to Codeforces Round #134!

After over two years, it is again my great pleasure to be the main problemsetter of a contest on Codeforces. Thanks a lot to Gerald for helping me organize the round. I hope you will enjoy solving the problems as much as we enjoyed preparing them for you.

Dynamic scoring will be used, but the problems will be ordered by their expected difficulty, from easiest to hardest. Are our predictions correct? I am eager to see. :-)

Good luck!

Update: The contest is over! Here are the results:

First division:

1. rng_58

2. panyuchao

   pieguy

3. tourist

4. Petr

5. ACRush

6. Zhukov_Dmitry

All contestants from the top seven solved three problems. Note that there was a tie for second place. :-)

Second division

1. dsbuaa

2. hqztrue

3. Gullesnuffs

In second division, seventeen contestants solved four problems. Nobody managed to crack E; it was also present in the first division as problem C, and proved tricky even for the experienced competitors.

Congratulations to the winners!

Hello everyone.

That is the 133th Codeforces round. Specially for the 2nd division. Contestants from the 1st division can solve the round out of competition.

Round is prepared by Ripatti , Gerald , Aksenov239 , Delinur and MikeMirzayanov .

The round will use dymanic scoring system. Problems will be ordered in random manner (see UPD1). If you want get more happiness from solving that round, please, read statements of all problems.

Good luck!

UPD1. Jury members discussed and have decided to rearrange problems in expected order of difficulty.

UPD2. Contest ended. Winners:
1. karensun522
2. stostap
3. sisterX
4. BiliBili
solved all 5 problems. Congratulations!

Editorial will be soon tommorow (I am very tired =_=, but now you can try to read russian editorial here).

UPD3. Editorial in English.

Hi!

A few hours later you're lucky to participate in Codeforces Round #132 for Div.2 participants, but traditionally the others can take part out of the competition. It has been prepared by me (NALP), Edvard Davtyan (Edvard), Vitaly Aksenov (Aksenov239), Gerald Agapov (Gerald), Mary Belova (Delinur) и Mike Mirzayanov (MikeMirzayanov).

Traditionally I wish good luck, accepted solutions and successful hacking attempts for you!

Especially, we want to wish grand results and good luck to all sportsmens, who are representing their countries on XXX Olympic Games in London!

Today it is decided to use dynamic scoring system. But the problems will be sorted from low difficulty to high by authors' opinion!

UPD: The Round is finished, thanks to all for participation! We hope you have got fun!

UPD: Congratulation to winners!

1. yooo — solved all problems!

2. zzy

3. High_Rich_Handsome

4. bookcity_clock

5. capythm

UPD: Tutorial in English is published!

Hello everybody!

Welcome all to Codeforces Round #131, which will be held on Monday, 30th of July at 19:30 MSK. I am (Sergey Nagin) an author of the problems. This will be my First Codeforces round and I hope it won't be the last one :).

I would like to thank Mike Mirzayanov(MikeMirzayanov) who made this contest possible, Roman Furko(Furko) and Gerald Agapov(Gerald) for helping to prepare this round and Maria Belova(Delinur) for the translation of problem statements into English. I hope that problems will be interesting for you.

Good luck!

Problems’ point values in Division 1 are 1000-1000-1500-2000-2500. Problems’ point values in Division 2 are 500-1000-2000-2000-2500.

I strongly recommend you to read ALL the problems.

The contest is over! Congratulations' to winners!

First division:
1 place: Egor
2 place: Petr
3 place: tourist
Second division:
1 place: antimatter
2 place: c175353
3 place: takaramono

I hope, that problems were interesting for you.

You can view tutorial.

Welcome, friends)

We are glad to introduce you regular Codeforces round #130 for Div.2 participants. Everyone can traditionally participate in it. There were some problems with registration of Div.1 participants, but now everything is alright)

Problems are prepared by command of authors: Pavel Kholkin (HolkinPV), Nikolay Kuznetsov (NALP) and Gerald Agapov (Gerald). Traditionally thanks to Michael Mirzayanov (MikeMirzayanov) for perfect Codeforces system and Mary Belova (Delinur) for translating problems. Also thanks to Alexander Kouprin (Alex_KPR) and Pavel Kunyavskiy (PavelKunyavskiy) for their help.

And again score distribution will be dynamic) More information you can find here.

Note that all problems will be given in random order.

We wish you good luck, successful hacks and high rating!

UPD: the contest is over, no matter what, we hope you enjoyed the competition

UPD2: The authors apologize for the situation with the problem E. The problem has affected a small number of participants from div2 (22 participants) and the solution of original version of the problem doesn’t differ a lot (in most solutions is sufficient to remove a couple of lines, solutions become more simple). Therefore, it was adopted the following decision:

• for all 22 participants,who has problems with problem E and will have decrease of rating, the round is unrated.
• for everybody else the round is rated

UPD3: after recalculation it was found that there are 20 such participants, not 22

UPD4: unsuccessful hacks, which answers differed from the correct whitespaces, are decided to ignore

UPD5: tutorial can be found here

Today is the main VK Cup event: VK Cup 2012 Finals! Good luck to all participants. And to those who don't participate — enjoy the interesting competition. VK CEO Pavel Durov announced the upgrade of a prize fund in the greeting speech at the finals' opening! I'm starting to really regret that I am not a participant.

The participants compete for:

• 1st place — $30000
• 2nd place — $20000
• 3rd place — $10000
• 4-5 places — $2000
• 6-10 places — $1000

Good luck! Wish you only positive emotions. Ready! Steady!...

UPD: The contest is over! I believe Alex_KPR will write about the contest and the closing ceremony soon. Thank you for participation and your interest. Here are the complete standings.

Congrats to the winners. The top-3 is:

• sevenkplus (Yuzhou Gu) China
• s-quark (Qinshi Wang) China
• tourist (Gennady Korotkevich) Belarus

UPD: As you have already noticed, the 16th July at 19:00 will start an unofficial online-version of the VK Cup 2012 Finals. Anyone can participate and feel himself as a finalist. Round will be unrated. If you already took part in the Finals or familiar with the problems, please refrain from participation. All problems will appear in the archive and will be available to everyone.

Hi everybody!

Today, on the 14th of July, we hold a trial round of the VK Cup 2012 final championship round. The Codeforces functionality is very limited for the external visitors and for the finalists. Please stay calm.

The participants of the Finals do not have to register for the round. There are no special pep talks — you will face the familiar system with the usual settings. Oh yes, the system of assessing tasks will be dynamic. Let me remind you that you should not use any electronic devices or personal records, communicate with each other et cetera. You shouldn't violate any rule Codeforces and VK Cup rules. Tomorrow is a big day, let's rehearse it in all details.

MikeMirzayanov and the VK Cup 2012 jury team

Hi!

Time brings to you next Codeforces round, this time it is with number 129. It will take place in 11.07.2012 at 19:30 (Moscow time). This time the problems are authored by me, Vitaliy Herasymiv. Long time ago I was the author of 4 Codeforces rounds, they were about lucky numbers. But, unfortunately, nothing is constant, so this time there will be no problems about lucky numbers.

A lot of help in preparing of the problems was from Gerald Agapov (Gerald), Alexander Kouprin (Alex_KPR), Vitaly Aksenov (Aksenov239), The problems were translated to English by Maria Belova (Delinur). Thanks to all of them.

I hope you will like this all.

Good Luck!

Div1:

Thanks all! The results are the following:

1. tourist (now tourist become first Codeforces target, congratulations to him)
2. winger
3. RAVEman
4. rng_58
5. RAD
6. bmerry
7. Shik

Div2:

1. xiaoshua2
2. ahm.kam_92
3. HanzhongBall_Quanling
4. daidailanlan

You can read editorials here.

Hi everybody!

The VK Cup 2012 programming championship finals is going to take place very soon. The organizing committee and jury are working around the clock to set up the event that the participants will like.

Let us remind you that the finals will take place from July, 13 to July, 16. We will choose the best 50 participants by the results of VK Cup 2012 Round 3. As soon as we are absolutely sure about who can come to the finals, we will publish the list of the finalists.

We’d like to share some information from the organizing committee headquarters. The finals’ participants will be accommodated in the beautiful Kempinski hotel in the centre of St. Petersburg, on the bank of the Moika. The hotel is located within a walking distance from the Vkontakte office, so there won’t be any exhausting buses and coming across the city’s traffic jams! Please note the roof restaurant with the view on the Palace Square when you take a look at the photos of the hotel.

There is no exact timetable yet, something depends on the time when the participants will arrive and the complexity of the problems (that’s right, the final round may not have the usual timing). The general plan is as follows:

• July, 13: Checking in, having dinner, meeting each other and having fun.
• July, 14: Most of the day will be dedicated to an unofficial entertaining event called Code Game Challenge (special for VK Cup 2012). Also a short testing tour is planned on that day. In the evening the great dinner will be topped with Code Game Challenge Show – watching the strategy tournament on a large screen.
• July, 15: The main day of the competitions (good luck!). In the evening we’ll reward the winners and celebrate all finalists (I am sure that everyone will be pleased :));
• July, 16: Going home.

Vkontakte and Codeforces are very glad to see the students’ interest in VK Cup 2012. Despite us inviting only young coders to the championship (the age limit should not exceed 23 years), nearly 6000 participants registered there. They geographically cover practically all countries of the world! We are very glad to see that almost all coders who advanced to the finals could make it to St. Petersburg. The winners will get worthy awards, and at this point we are happy to announce that the championship prize fund has been increased! You’ve got an aim to fight for and do your best to win!

• 1st place — $20000
• 2nd place — $10000
• 3rd place — $5000
• 4-5th place — $2000;
• 6-10th place — $1000.

Easy journey to the finalists,
The VK Cup 2012 jury and organizing committee.

Questions and Answers

• What will be the rules of the Final Round? The round will be held by the rules of Codeforces, it will be 2 or 2.5 hours long. The dynamic problems' scoring is likely to be used.
• Will we use the PCs that you will give us, or our own PCs? The participants will use special workstations prepared by the VK Cup Team. It is not allowed to use one's own laptops. You may bring a USB-keyboard, but it should not have superior features.
• What operation system will be used? We hope to give the oppotunity to boot Ubuntu 12.04 or Windows at the participant's choice. We are working on it now. We will install a wide list of free software on both OS.
• Is it possible to use a prewritten code? Basically no, it is only allowed to use the code written on the competition. But you may use the code written on the practice session or on the CodeGame coding phase.

Saint-Petersburg photos

Hello, friends!

A few hours later you're lucky to participate in this remarkable Codeforces Round #2⁷ for Div. 2¹ participants, but traditionally the others can take part out of the competition.

It has been prepared by a small band of authors: me (NALP), Igor Kudryashov (Igor_Kudryashov), and Pavel Kholkin (HolkinPV). There were Gerald Agapov (Gerald), Maria Belova (Delinur) and Mike Mirzayanov (MikeMirzayanov) with us as always.

It’s well-known that you can participate in this Round into competition only today! There won’t be another Codeforces Round #2⁷!

Traditionally I wish good luck, accepted solutions and successful hacking attempts for you!

UPD: Points are standard: 500, 1000, 1500, 2000, 2500.

UPD: Round is over, thanks to all! We hope you have got a fun. Don't forget, system testing will be soon.