From 16th to 22th May, Ukrainian Selection Camp for the EJOI (European Junior Olympiad in Informatics) and EGOI (European Girls Olympiad in Informatics) was held in Wrocław, Poland.

Thanks to University of Wrocław and gawry for the second time for help in organising the selections!

We are very grateful to Sergey Kolodyazhnyy for creating powerful online judge Eolymp.

Also, I would like to thank wasvlad for helping me in preparing problems. Maryna, Olena and Melissa Melissa_14 for looking after the participants and Federation of Olympic Programming of Ukraine presented by arsijo for coordinating the entire process.

So, on EGOI Ukrainian Team will be represented by:

• Daria perekopska.d Perekopska, 2 attempts left
• Kseniia ksu_ Strelbytska, 2 attempts left
• Yunna YKheifets Kheifets, 0 attempts left
• Viktoriia lavvikta Lavrova, 1 attempt left

Left to right: Daria, Viktoriia, Kseniia, Yunna

And on EJOI Ukrainian Team will be represented by:

• Maksym Umanity Shvedchenko, 0 attempts left
• Kseniia ksu_ Strelbytska, 0 attempts left
• Daria perekopska.d Perekopska, 0 attempts left
• Dmytro dimastrakhal Strakhal, 0 attempts left

Left to right: Dmytro, Kseniia, Maksym, Daria

As usual some photos of our delegation included =)

You can see full results of the selections via this link

I would like to notice, that this is the first time when Ukrainian EJOI Team would consist of two girls! Amazing!

Also, I would like to gratulate Maksym Umanity Shvedchenko with solving 3/3 tasks three days out of four, and Daria perekopska.d Perekopska with solving 3/3 tasks two days out of four! Incredible score!

I am very happy with our current generation and wish them good luck at upcoming competitions!

A few days ago, from 8th to 20th May, Ukrainian Selection Camp for the IOI (International Olympiad in Informatics), BOI (Balkan Olympiad in Informatics), EJOI (European Junior Olympiad in Informatics) and EGOI (European Girls Olympiad in Informatics) were held in Wrocław, Poland.

Thanks to University of Wrocław and especially to gawry for help in organising the selections. Contestants were very happy to visit one of the biggest Polish cities and to solve problems in one of the most modern spots for OI's in Poland.

Also, I would like to thank wasvlad for helping me in preparing problems for IOI and BOI selections, and to thank oleh1421 and timreizin for preparing problems for EJOI and EGOI selections, Maryna, Sofiia and Nastya for looking after the participants and Federation of Olympic Programming of Ukraine presented by BanRussiaAtIOI for coordinating the entire process.

So, on IOI Ukrainian Team will be represented by:

• Alisa Potomkina nhype
• Daryna Karpenko DJeniUp
• Andrii Smutchak xGaz_
• Andrii Stolitnii welleyth

Left to right: welleyth, DJeniUp, nhype, xGaz_

And, on BOI Ukrainian Team will be represented by:

• Alisa Potomkina nhype
• Andrii Smutchak xGaz_
• Denys Tereshchenko TheQuantiX
• Ihnat Zharikhin Ignut

Left to right: Ignut, TheQuantiX, nhype, xGaz_

On EJOI Ukrainian Team will be represented by:

• Kyrylo Redenskyi Relex
• Daria Lobas DaniraSilla
• Yurii Psiuk Psiuk_Yurii
• Andrii Basov BAD_353

Left to right: Psiuk_Yurii, BAD_353, DaniraSilla, Relex

On EGOI Ukrainian Team will be represented by:

• Daryna Karpenko DJeniUp
• Alisa Potomkina nhype
• Daria Lobas DaniraSilla
• Olha Volianyk OliaVolia

Left to right: nhype, DaniraSilla, OliaVolia, DJeniUp

The full results for the IOI and BOI selections are available here: https://camp23.eolymp.space/s/results

The full results for the EJOI and EGOI selections are available here: https://ejgoicamp23.eolymp.space/s/results

Some photos from Wrocław =)

Good luck to them at the upcoming olympiads!

Hello. I am from Ukraine. I am sure that you know about the situation in my country and about things happening right now. Many people are giving infinitely valuable help to Ukrainian refugees, donating to UAF and simply helping spread the truth. I am sure we have such people also in our community. Ukraine, Ukrainians, and personally I appreciate your help highly. Thank you so heartily.

But now I am here to ask you, the Codeforces community, for help. There is no safe place in Ukraine right now — everywhere you might get killed by a missile strike, so holding the IOI selections is obviously impossible. Our dear friends from Poland decided to help us. They will organise everything for us, but they need money.

→ Click here to donate ←

Ukrainian competitive programmers are one of the most powerful cp-eps in the World. Our the most recent achievements:

• Baltic Olympiad in Informatics — 4 gold medals, 2 bronze medals
• International Zhautyk Olympiad — 2 gold medals, 3 silver medals, 7 bronze medals
• Romanian Masters of Informatics — 2 gold medals, 1 silver medal, 6 bronze medals
• International Autumn Tournament in Informatics — 2 gold medals, 3 silver medals, 3 bronze medals
• European Girls Olympiad in Informatics — 1 gold medal, 3 silver medals
• European Junior Olympiad in Informatics — 4 silver medals, 4 bronze medals
• International Olympiad in Informatics — 1 gold medal, 2 silver medals
• All-Russian Team Olympiad among Scholars — 1st absolute place, it was the first time when Ukraine team become the winner of this competition and one of a few times that has received a medal.

and so on...

Participation in the IOI is the most wanted dream for every competitive programmer in school times and Russia is trying to break this dream for each of us. But you can help. Everything is in your hands. If everyone, who reads this post, donates about 1 euro, the fundraising will end in 24 hours.

We need your help. Thanks in advance.

→ Click here to donate ←

upd: if you can't donate, help at least in sharing this post

upd2: updated link in the post to English version of the website

upd3: thanks to everybody for helping in any way!

Do you play on a guitar? Does somebody among top coders play on a guitar? If you do, what is your favorite song? And, a little strange question, but which chord do you like the most?

Hmm, it's time to update year in CodeForces code. Again.

On today's CF Round #742, I submitted my code to the problem E, and suddenly got "Compilation Error", compile log informed me this thing:

Compiled file is too large [47861470 bytes], but maximal allowed size is 33554432 bytes [CompileRequest {id='program.cpp', description='', file='program.cpp', resources='', type='cpp.msys2-mingw64-9-g++17'}].

Submission: 127958200

I thought this is a system's bug, and resubmitted the code, and I got the same error: 127958576. After that, I saw that my binary file really is too large — about 44 Mb. I tried different things like getting rid of useless libraries or enabling optimization like Ofast/O3 etc. But none of this helped. After that, I wanted to replace all long longs except t_obj.ans with ints, but only separated ans from other variables and made tiny change ll ans=0; -> ll ans;, and compiled. It was really strange, but the binary file size became 36 Kb. To make me safe, I removed =0 from almost all variables and made a constructor, which makes them zero, and submitted that. It compiled well and passed pretests — 127960252.

So, the question is: how =0 near the variables can affect binary file size? This works only on GNU-based compilers? Can this behaviour be predicted, and can it be forced? Can I in such way reduce work time by increasing compile time?

Sorry for my bad English, thanks for any answer.

ошиете ошиете йо

боку но нака ни, даре га иру но.

Hello Codeforces, recently, there was a contest on CSAcademy named "FiiCode 2021 Round 2" and there was a task "Clown Fiesta", in a editorial for the task, there were lines such like:

If we take a sequence, where $$$a_0 = m$$$, $$$a_1 = \varphi (a_0)$$$, $$$a_2 = \varphi (a_1)$$$, $$$...$$$, $$$a_{k-1} = \varphi (a_{k-2}) \neq 1$$$, $$$a_k = \varphi (a_{k-1}) = 1$$$ and $$$m$$$ is prime number less than $$$10^9$$$, then $$$k$$$ will be not greater than $$$log_2(m)$$$.

Can someone prove it?

P.S. link to problem.

Сегодня MikeMirzayanov сделал улучшение codeforces'-а которое должно было как-то улучшить его работу. Ввелось кучу новых серверов типа s5.codeforces.com, благодаря которым, загрузка codeforces в Украине даже с включённым vpn это 1 минута ожидания. МАЙК СДЕЛАЙ ЧТО-ТО Я ТЕБЯ УМОЛЯЮ Я ЖИТЬ БЕЗ КФА НЕ МОГУ!!!!!!!!!!!!!!!

Hello, Codeforces. Today I solved problems in problemset and found interesting thing. Well known that when you create problems in polygon you can set custom output to tests in statements. It is used in many problems where you must output algorithm to solve. But, when you submit your code, you can see your output to test and jury's answer. The custom output on examples is used so that the participant does not understand the algorithm for solving by examples, but the jury's answers can lead the participant to the correct algorithm. For example, lets see second test from problem 1479C - Continuous City.

The output in statements:

The output in submission:

As we can see, outputs differ. I think this is serious bug, which can lead participants to jury's algorithm, and this should be fixed asap

MikeMirzayanov It's time to make year++ in CodeForces code :))

upd: it`s fixed now!

Всем привет! Нашел одну интересную задачу: ссылка Кто-нибудь знает как её решить?

Доброго времени суток всем! Подскажите, есть ли какие-то YouTube-каналы с разбором сложных задач с Codeforces или других сайтов? Можно чтобы были и не на русском языке.