Today I'll be the author for this round, and it's my first time to be an author in Codeforces. I hope you will like the problems and find it interesting, even for Div1 coders.
I would like to say thanks for Artem Rakhov for solving and testing the problems, for Maria Belova for preparing the problem statements, and for Mike Mirzayanov for this great system.
Good luck and have fun.
Edit 1: Congratulation to the winner Chubcheg.
Edit 2: The problem editorial is here.