Christmas calendars are very popular in western countries. This is usually a special board with windows corresponding to the days from December 1 to December 24, each of which contains a candy or small souvenir. In this case, every day opens the task of programming, consisting of two parts - simpler and more complicated. An excellent reason to stretch your brains or learn a new language.
Last year's Habr's standings are still active, eight people already participate in it this year. Everyone else can join by entering the code: ')
55074-c2e83c69
PS If you share tips on solving problems in the comments, do not forget to use those <spoiler>!