Hello, Codefoolers!

We, AlperenT, Ari, ToxicPie9, flamestorm, prvocislo, temporary1, and willy108 would like to invite everyone on Codeforces to April Fools Day Contest 2026! The 14th April Fools Day Contest will take place on Apr/01/2026 17:35 (Moscow time). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round, you will be given $$$n$$$ problems where $$$n$$$ is the number of different AI models I used today and 2 hours to solve them. The contest will use extended ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise.

There will be at least one non-interactive problem. In case you do not care about those problems, here is the guide for interactive problems.

Please note that the round is unrated and that the penalty for a wrong submission is 10 minutes. Furthermore, similar to other contests, it is not allowed to use AI help unless permitted in this blog.

To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025, 2026. (Does anyone ever click these anyway, why do I have to keep adding them each year?)

Thanks to our precious testers:

ChatGPT, Gemini, Claude, Grok, DeepSeek, and a few others who preferred to remain anonymous.

It is, without a doubt, the least enjoyable part of April Fools for us to respond to clarification requests with funny responses. It is certainly not the main motivator for us to prepare these contests in the first place. Therefore, please refrain from continuing this tradition.

Good luck, and have fun!

Update 1:

Editorial is released!

Update 2:

Congratulations to the winners:

1. ksun48
2. SeptaCube
3. pwild
4. 0x0c5cbae8
5. ishmeal

And the first solves on each problem (after blatant cheaters):

• A: shash4321 — 0 minutes
• B: ksun48 — 0 minutes
• C: jdurie — 4 minutes
• D: thespace — 3 minutes
• E: ksun48 — 4 minutes
• F: SeptaCube — 13 minutes
• G: bronze_coder — 51 minutes
• H: circle977 — 1 minutes
• I: Egg_Knight — 33 minutes
• J: Nagerhide — 11 minutes

Hello Codeforces!

Since the ICPC World Finals 2025 is approaching fast and the invitations seem to be sent, I decided to post a blog to gather Codeforces handles as I couldn't see one for this year.

Please write a comment with the team informations and I will add them to the post.

It would be great if you write the comments using this template:

Handles (or names), Region, Country, University

Asia East:

North America:

Northern Eurasia:

Europe:

Asia Pacific:

Asia West:

Africa and Arabia:

Latin America:

• To request update to a team rating, please leave another comment.

Hi Codeforces!!!

As in the last three years, we are very excited to invite IOI 2025 participants and leaders to the International Olympiad in Informatics Discord server!

This server is a great place to meet new people who are also participating in the Olympiad, make plans with them, share advice, practice together, or simply chat about random topics! The server also has multiple useful bots, such as TLE and Contest Reminder, that you can use to practice for the olympiad or simply have fun.

The server currently has:

• Committee Members: 13
• Team Leaders: 79
• IOI 2025 Participants: 146
• IOI 2024 Participants: 204
• IOI 2023 Participants: 195
• IOI 2022 Participants: 196
• Past IOI Participants: 132

If you are or were an IOI delegation member, please feel free to become a part of the community using the following link.

Hello, Codefoolers!

We, AlperenT, flamestorm, prvocislo, temporary1, ToxicPie9, and -1e11, would like to invite everyone on Codeforces to April Fools Day Contest 2025! The 13th April Fools Day Contest will take place on 01.04.2025 17:35 (Московское время). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round, you will be given $$$n$$$ problems where $$$\sum\limits_{x=1}^{\infty} \frac{1}{x^n}$$$ converges and 2 hours to solve them. The contest will use extended ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise.

Please note that the round is unrated and that the penalty for a wrong submission is 10 minutes.

To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024

Thanks to our precious testers (they exist, trust me):

Please do not bother sending clarification requests in the contest as we obviously do not enjoy sending funny responses like we did in the last two years. It is definitely not the most fun part of April Fools.

Lastly, we have a video editorial this year (Russian captions available)!

Good luck, and have fun!

Edit 1: Editorial is out!

Edit 2:

Congratulations to the winners:

1. ksun48
2. Madball
3. iakovlev.zakhar
4. tiger2005
5. errorgorn

And the first solves on each problem:

• A: vladimirfilip
• B: Auchenai01
• C: Dark (after AprilFoolsClairvoyant)
• D: koishi.komeiji
• E: jiangly
• F: tiom4eg
• G: BucketPotato
• H: N/A (but circle977 got closest with every word except 10th)
• I: SeptaCube
• J: fishy15 (initially conqueror_of_tourist, but got hacked after the contest)

Hello, April Fools lovers Codeforces!

We, AlperenT, flamestorm, ToxicPie9, and willy108, would like to invite everyone on Codeforces to April Fools Day Contest 2024! The 12th April Fools Day Contest will take place on Apr/01/2024 17:35 (Moscow time). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round, you will be given $$$n$$$ cool bugaboos where $$$-1 \le n \le \textbf{[REDACTED]}$$$ and 2 hours to solve them. The contest will use extended ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise.

Please note that the round is unrated and that the penalty for a wrong submission is 10 minutes.

To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023. (It has been 12 years since the first April Fools Day Contest, thank you Nickolas!)

Please do not send any clarification requests in the contest, as we definitely will not be sending funny responses like we did last year.

Good luck, and have fun!

UPD: Editorial is released!

UPD: Congrats to the winners:

1. tiger2005
2. emthrm
3. Enchom
4. arvindf232
5. KumaTachiRen

And the first solves on each problem:

• A: InternetPerson10
• B: Mr_Buffon
• C: Thienu
• D: moraprex
• E: BalintR
• F: SanguineChameleon
• G: 7_divided_by_3
• H: Owmicron
• I: JJJiang.is.MyGO
• J: Joshc

Hello Codeforces!

As last year, we are happy to invite IOI 2023 participants and leaders to the International Olympiad in Informatics Discord server. We currently have around 75 members from 2023, 190 from 2022, 100 from past IOIs, and 25 team leaders.

This server is a great way to get to know new people who are also participating in the Olympiad, make plans with them, share advice, and even practice together! The server also has multiple useful bots including TLE and Contest Reminder.

If you are or were an IOI delegation member, please feel free to become a part of the community using the following link.

Thank you for participating in our contest! We hope you enjoyed it.

Please let us know what you thought of the problems by voting!

1812A - Вы робот?

Idea: ToxicPie9
Preparation: flamestorm

1812B - Was it rated?

Idea: BucketPotato
Preparation: BucketPotato

1812C - Цифры

Idea: ToxicPie9
Preparation: ToxicPie9

1812D - Тривиальная гипотеза

Idea: AlperenT
Preparation: AlperenT

1812E - Не задача по геометрии

Idea: ToxicPie9
Preparation: ToxicPie9

1812F - Факторизация

Idea: flamestorm
Preparation: flamestorm

1812G - Цветовое зрение

Idea: flamestorm
Preparation: flamestorm

1812H - Ожидаемое твист

Idea: ToxicPie9
Preparation: ToxicPie9

1812I - Скалолаз

Idea: Ari
Preparation: Ari

1812J - Не-загадочный язык

Idea: ScarletS, ToxicPie9, et al.
Preparation: ToxicPie9, ChatGPT

I fell to candidate master after the contest TypeDB Forces 2023 (Div. 1 + Div. 2, Rated, Prizes!). However, just before the contest Codeforces Round 848 (Div. 2), there was a rating rollback, and I became master again. Because of this, I had to register for Div. 2 as out of competition. I was expecting this to be calculated but seems like it didn't because others had a rating change while I didn't. If it's possible, can this be fixed please?

Hello Codeforces!

SlavicG and I have put together the "International Olympiad In Informatics" discord server! The server is aimed to be a place where the IOI community can chat, relax, make plans, share pictures, give and receive advice, help each other and of course, have fun! IOI participants and any other delegation members from any year are welcome on the server!

If you fit in any of the categories feel free to join the server using the following link.