Welcome to another Codeforces Round!
Please note that the time of round #191 was changed. Contest will start at Thursday 12:30 UTC.
My name is Linh (ll931110). I'm from Vietnam, and I'm glad to present to you my first Codeforces round. It is for Div 2 only; however, I welcome participants from Div. 1 to participate and enjoy challenging problems. I hope this would be a pleasant gift for those who are going to IOI 2013 (and participants from World Finals), which will take place in just a couple of days.
This round is prepared by me and florin.elfus (from Romania). Also, I would like to thank the Codeforces team who puts efforts on making Codeforces and Polygon possible.
UPD1: The score of problems in this round will be dynamic. The problems will be sorted in increasing difficulty order, at least in our perspective.
UPD2: The contest is over! Congratulations for everybody, especially for those who solved E. You proved to be smarter than I am (your solutions were totally unexpected to us). Thank Gerald, Aksenov239 and Delinur for helping us on preparing the round!
Div. 2 winners:
Those are five people who nail all problems!
The editorial will be completed soon after revising and adding possible alternative solutions. You are welcome to post your answers in comments.
Thank you and see you in the next round!
UPD3: Editorial is now available. Remind that it is not the final version, as we are writing possible alternative solutions for problems. Stay tuned!
UPD4: Editorial is now completed.