Hi Codeforces!

Every beginner here at least once wondered: "what to do to increase the rating?" The most common answer was to solve the archive. Immediately, the error of every newcomer surfaced: he chose the easiest tasks, solved them and did not develop at all. Or the opposite situation: He immediately took on complex tasks, did not understand anything and abandoned this business.

This is what this post was created for! What tasks do you think are the most interesting / common? What tasks should every beginner / specialist / expert solve at least once?

 It is desirable that after these tasks it should be like this :D