Codeforces has an excellent archive of training contests, named gyms!

But it is very well possible that you do not know about the one gym that I want to cover today, and the reason is that it is only available in Russian :|

I translated the statements to English for you, and recorded a problem walkthrough with theoretical material included, in case you ever get stuck or want to refresh the theory.

We will cover more gyms from this old but gold series by Saint Petersburg State University in the future, so stay tuned!

Also Happy New Year to everyone who will see this on Jan. 1!