Hello, Codeforces!

Educational Codeforces Round 13 will take place on 13 June 2016 at 19:00 MSK for the first and the second divisions. Almost two months passed from the previous round. That is due the next reasons: 1) I coordinated regular CF-round at the end of April; 2) about whole CP community were busy with preparing and competing in ACM ICPC WF in May; 3) at the beginning of this month I start to work at AimTech (I hope that I'll have enough time to continue prepare ERs).

<It's need to read at least once maybe you'll find something interesting>

The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

If you have ideas for some problems or maybe already prepared problems that you can't use in rounds or official competitions, you can write to me.

It seems that it is harder to invent interesting simple problems (like A and B) than difficult ones. So don't be afraid to suggest interesting simple or very simple tasks (of course the difficult tasks are also needed). Please send only the problems for which you know the solution with clear statement (the story is not required). And also please add one or two samples to make the problem statement more clear.

</It's need to read at least once maybe you'll find something interesting>

The problemset was suggested by Codeforces users. The problem А was suggested by user Abdrakhman Ismail bash. The problem B was suggested by Arthur Jaworski KingArthur. The problem C was suggested by Sheikh Monir skmonir. The problem D was suggested by Zi Song Yeoh zscoder (there are a lot of unused his problems). The problem E was suggested and prepared by Alexey Dergunov dalex. The simpler version of the problem F was suggested by AmirMohammad Dehghan PrinceOfPersia.

Thanks a lot to them and all others who are sending the problems! The number of unused problems are increasing. If I didn't miss anything I already replied to all who sent me the problems at least 5-6 days ago. Please be patient if your problem was not used a long while.

As I said the problem E is prepared by Alexey Dergunov dalex. All other problems was prepared by me (Edvard Davtyan). Thanks to Tatiana Semyonova for checking the English statements. The problems was tested by users suggested them, respectively: Abdrakhman Ismail bash, Arthur Jaworski KingArthur, Sheikh Monir skmonir, Zi Song Yeoh zscoder, Alexey Dergunov dalex and AmirMohammad Dehghan PrinceOfPersia. Thanks a lot to all of them!

I hope you will enjoy the problems! Previous time the problems were too hard. I've tried to fix that. The problems should be simpler than usual.

Good luck and have fun!

It's the first summer round :-)