Hello Codeforces!

Every month, there will be a problem with complete explanations and solutions for one of the month's problems. Here is the problem of February. Feel free to ask me questions and suggesting edits.

Please help me by proposing a problem for the next month. In the November contests, look for a challenging problem that you would like to have complete explanations of it.

Also, what do you think about video tutorials instead of text editorial?