Thanks for the participation!

1181A - Chunga-Changa was authored by vintage_Vlad_Makeev and prepared by achulkov2

1181B - Split a Number was authored by Endagorion and prepared by manoprenko

1181C - Flag was authored and prepared by budalnik

1181D - Irrigation was authored by Helen Andreeva and prepared by ch_egor

1181E2 - A Story of One Country (Hard) was authored by voidmax and prepared by voidmax and alexey_kuldoshin.

And now the editorial:

Hi!

Tomorrow 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 and, of course, Helen Andreeva.

We are happy to announce the codeforces round based on the problems of this olympiad! It will be a Div. 2 round, which will take place at Jun/16/2019 12:35 (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)

The problems of this olympiad were prepared by voidmax, alexey_kuldoshin, ch_egor, budalnik, achulkov2, manoprenko, vintage_Vlad_Makeev, Endagorion.

Thanks KAN for his help in organizing the Codeforces version of this contest and MikeMirzayanov for the Codeforces and Polygon.

Also I would like to thank the Tinkoff company and personally Tatyana Kolinkova for organizing the onsite competition.

Good luck!

Scoring: 500-1000-1500-1750-(2000+750)

upd. Congratulations to winners!

Div. 2:

1. thecodinglizard
2. baIuteshih
3. Cong1500DanPaiXia0
4. Yelan
5. HatsuneMikuo

unofficial Div. 1:

1. Radewoosh
2. isaf27
3. chemthan
4. uwi
5. kmjp

The editorial will be published soon.

upd. the editorial was published.

Credits:

1138A - Sushi for Two, idea and development by KAN

1138B - Circus, idea by MikeMirzayanov, development by cdkrot

1137A - Skyscrapers, idea by jury together, development: achulkov2

1137B - Camp Schedule, idea and development by wrg0ababd

1137C - Museums Tour, idea by ch_egor, development by qoo2p5

1137D - Cooperative Game, idea and development by mingaleg

1137E - Train Car Selection, idea and development by Schemtschik

1137F - Matches Are Not a Child's Play , idea by GlebsHP, development: cdkrot

And now the editorials:

Hello!

Right now happens the first tour of the Open Olympiad in Informatics, and tomorrow will be the second one. This contest is prepared by Moscow Olympiad Scientific Committee that you may know by Moscow Team Olympiad, Moscow Olympiad for Young Students and Metropolises Olympiad (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541)

Open Olympiad consists of the most interesting and hard problems that are proposed my a wide community of authors, so we decided to conduct a Codeforces regular round based on it, which will happen Mar/08/2019 12:05 (Moscow time) and will be based on both days of the Olympiad. Each division will have 6 problems and 2:30 hours to solve them.

We kindly ask all the community members that are going to participate in the competition to show sportsmanship by not trying to cheat in any manner, in particular, by trying to figure out problem statements from the onsite participants. If you end up knowing some of the problems of Moscow Open Olympiad (by participating in it, from some of the onsite contestants or in any other way), please do not participate in the round. We also ask onsite contestants to not discuss problems in public. Failure to comply with any of the rules above may result in a disqualification.

Problems of this competition were prepared by vintage_Vlad_Makeev, isaf27, Flyrise, cdkrot, GlebsHP, ch_egor, Zlobober, qoo2p5, grphil, achulkov2, Schemtschik, akvasha, mingaleg, V--o_o--V, wrg0ababd, guided by ch_egor, cdkrot, GlebsHP, Zlobober and Helen Andreeva.

Problems for second division were prepared by KAN and MikeMirzayanov, to who we also want to say thanks for the Codeforces and Polygon systems.

Good luck everybody!

UPD: Congratulations to the winners!

Div.1

1. sunset
2. Petr
3. Radewoosh
4. ko_osaga
5. orbitingflea

Div.2

1. appplese
2. al3xstr33t
3. Charlene_Hao
4. ytxytx
5. QDEZ604

The editorial will appear soon

UPD: The editorial

The round has finished. I hope you liked it!

Credits to the round authors and developers:

1110A - Parity. Authored by _h_ and simonlindholm.

1110B - Tape. Authored by _h_ and simonlindholm, development: cdkrot

1110C - Meaningless Operations. Authored by GreenGrape

1110D - Jongmah. Authored by _h_ and simonlindholm, development: KAN and MikeMirzayanov

1110E - Magic Stones. Authored by _h_ and simonlindholm, developed by GreenGrape

1110F - Nearest Leaf. Authored by grphil, developed by vintage_Vlad_Makeev

1110G - Tree-Tac-Toe . Authored by cdkrot and KAN

1110H - Modest Substrings. Authored by _h_ and simonlindholm, development: budalnik

And now, the editorial:

Credits:

Div2A (Make a Trianle): Idea by Zlobober, development by vintage_Vlad_Makeev

Div2B (Equations of Mathematical Magic): Idea and development: Glebodin

Div1A (Oh Those Palindromes): Idea by Endagorion, development by Andreikkaa

Div1B (Labyrinth): Idea and development by qoo2p5

Div1C (Dwarves, Hats and Extrasensory Abilities): Idea and development by mingaleg

Div1D (Candies for Children): Idea by Endagorion, development by Flyrise

Div1E (Lasers and Mirrors): Idea and development by mingaleg

Div1F (String Journey): Original idea by GreenGrape, solution by vintage_Vlad_Makeev, development vintage_Vlad_Makeev and GreenGrape

Div2A ("Palindrome Dance") was authored by jury members altogether, development: darnley

Div2B ("Skewers") was authored by jury members altogether, development: GlebsHP, Codeforces hardened version: KAN.

Div1A ("Timetable") was authored by Zlobober and meshanya, development: kraskevich.

Div1B ("Subway Pursuit") was authored by V--o_o--V, development: wrg0ababd

Div1C ("Network Safety") was authored by V--o_o--V, development: achulkov2.

Div1D ("You Are Given a Tree") was authored by GlebsHP, development and codeforces edition cdkrot, faster model solution: V--o_o--V.

Div1E ("Summer Oenothera Exhibition") was authored by Zlobober, development by malcolm.

Some editorials are being published, please wait a bit :)

Hi everybody!

These days Moscow is conducting the 3rd International Olympiad of Metropolises that is an international competition for high school students from biggest cities and capitals all around the world. One of the disciplines of the competition is informatics. Rounds of the competition were prepared by the jury members invited from St. Petersburg, Minsk, Belgrade and Moscow olympiad scientific committee which you may know by Moscow team Olympiad, Open Olympiad in Informatics and Moscow Olympiad for young students (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469).

Scientific Committee of the olympiad consists of: darnley, Endagorion, Jelena Hadži-Purić, Elena Andreeva, Zlobober, GlebsHP. The problems were developed by kraskevich, ch_egor, cdkrot, Schemtschik, GoToCoding, malcolm, akvasha, darnley, wrg0ababd, achulkov2, vintage_Vlad_Makeev under the guidance of GlebsHP and Zlobober.

Problems were adapted for codeforces by KAN and cdkrot, also thanks for MikeMirzayanov for systems codeforces and polygon, which was used to prepare problems of this olympiad. Also, thanks LHiC and V--o_o--V for testing!

Good luck and high ratings for everybody!

Round will happen on Sep/05/2018 19:35 (Moscow time) and will last for two hours. There will be 5 problems for each division.

P.S. We kindly ask everybody who knows problems of an onsite event not to participate in a round and not to discuss them in public, as this may be a subject for disqualification.

Upd: Editorial was published here!

Aaaand congratulations to winners!

Div1:

1. Um_nik
2. 300iq
3. webmaster
4. ksun48
5. Anadi

Div2:

1. GSHSIF
2. gosuto
3. Onjo
4. sturdyplum
5. LYJabc

Thank your for participation!

Problem D2A (New Building) was authored and prepared by Burunduk2.

Problem D2B (Badge) was authored and prepared by me, the version in SIS's olympiad contained the version with n ≤ 10⁵.

Problem D1A (Elections), D1B (Hat), D1D (Large Triangle) were authored by achulkov2, with D1A prepared by Schemtschik, D1B by achulkov2 and D1D prepared by achulkov2 and craborac.

Problem D1C (Sergey's Problem) was authored and prepared by Morokei.

Problem D1E (Raining Season) was authored and prepared by izban.

Editorials were written by izban and VArtem

Hi!

Summer Informatics School (SIS / LKSH) is a summer school for students in grades 6-10. SIS is focused mainly (but not only) on students participating in the Olympiads in Informatics — from beginners to participants of international competitions. SIS is held in July and August, each of them is visited by about 200 students from all over Russia and abroad. The language of the camp is Russian. Additional information about SIS is posted at lksh.ru

Right now, the August branch of the Summer Computer School is running, and on August 11 the traditional team Olympiad is going to place. I am happy to present a rated round based on it!

The round will be rated for both divisions, will be held in Aug/11/2018 16:35 (Moscow time), in each division there will be 5 tasks and 2 hours to solve them.

The problems of this round and the SIS olympiad were authored and prepared by SIS's teachers: izban, achulkov2, Schemtschik, peltorator, craborac, asokol, Morokei, Burunduk2. Also, I would like to thank Kurpilyansky for his help with olympiad's organization.

Thanks to our problems testers: meshanya, Burunduk2, vintage_Vlad_Makeev, niyaznigmatul, manoprenko!

Thank you, MikeMirzayanov, for the codeforces and polygon systems!

Yes, we are aware, that this contest clashes with ProCon Junior on codechef. However, given the schedule of the SIS and the approaching VK cup finals we can't do anything with it, sorry for that =/

Good luck!

UPD: The round will have one interactive problem for both divisions. Please, read the post about interactive problems here: Interactive Problems: Guide for Participants.

Congratulations to winners!

Div1:

1. Marcin_smu
2. Radewoosh
3. Swistakk
4. Panole233
5. ko_osaga

Div2:

1. wnsh
2. aurelio
3. usachevd0
4. jebouin
5. etiennerossignol

Upd Thank you for participation! Due to vk-cup conduction rating recalculation will happen slightly later, than usually.

Upd The editorial is published!

You may also check the unofficial editorial, written by neal.

D2A author: 300iq, cdkrot, developer: 300iq

D2B author: isaf27, developer: cdkrot

D1A author: isaf27, developer: isaf27

Jury's solution (isaf27): 40973089

D1B author: 300iq, developer: Flyrise

D1С author: pashka, developer: cdkrot

D1D author: tourist, developers: qoo2p5, VArtem

The first solution: 40971595 and the second solution: 40971634.

D1E author: isaf27, developer: isaf27

Jury's solution (by isaf27): 40973023

D1F author: GlebsHP, developers: demon1999, PavelKunyavskiy

Credits to all jury members, who contributed to this round and EJOI: tourist, PavelKunyavskiy, niyaznigmatul, 300iq, GlebsHP, pashka, qoo2p5, VArtem, demon1999, Flyrise, ifsmirnov, isaf27, yeputons, cdkrot.

Unfortunately, we had a bug in our interactor of the interactive problem.

The interactor contains the following code:

if (y < x)
    t = -1;
else if(y > x)
    t = 1;
else
    t = 0;
if(!p[q % n])
    t *= -1;
cout << t << "\n" << flush;

This is the opposite to the statement. However, it turns out that this error doesn't causes any harm for solving problem — it actualy just inverts the pattern, selected by judges. This also wasn't noticed during testing, by the same reason — the error is not visible to the user code.

But it may cause unexpected behaviour for hackers -- since they write the pattern themselves.

We are very sorry for this error and decided to do the following:

• The round will be rated, because very little people (maybe even zero) got affected (the people, who made incorrect hack)
• If you made a hack, which turned to be incorrect due to the error, we will cancel your  - 50 points and recalculate your rating afterwards. Please PM me if you have such a hack.

We are very sorry again. This is a huge lesson to us to be more attentive.

I hope you enjoyed the round!

Hi, codeforces!

I am happy to invite you to the codeforces round #493, which happens at Jul/01/2018 17:05 (Moscow time).

This round writers are — Ildar 300iq Gainullin, Grigory vintage_Vlad_Makeev Reznikov, Mike MikeMirzayanov Mirzayanov, and me, cdkrot.

Big thanks for people, who tested round — Shiqing cyand1317 Lyu, Andrew GreenGrape Rayskiy, Ivan isaf27 Safonov, Alexey Aleks5d Upirvitsky. Also thanks to Mike MikeMirzayanov Mirzayanov and Nikolay KAN Kalinin for help with round preparation.

And to Mike MikeMirzayanov Mirzayanov for codeforces and polygon systems.

Traditionally, there will be 5 problems for 2 hours. I hope you will enjoy the problemset, good luck and have fun!

Scoring distribution will be published before the round.

UPD: Scoring distribution is as follows:

Div1: 500 1250 1500 2500 3000

Div2: 500 1000 1250 2000 2500

You may also want to check this post for post-contest stream.

UPD2: The editorial was published!

UPD3: Congratulations to winners!

Div1:

1. TLE
2. ksun48
3. fateice
4. Swistakk
5. Um_nik
6. Petr
7. V--o_o--V
8. consecutivelimit
9. LHiC
10. uwi

Div2:

1. kirisamejin
2. liu_runda
3. AntiLeaf
4. TheFallenOne
5. haj_lemon
6. st-Firdavs
7. traxex
8. paladin
9. kmyiu
10. Maxim