Nim is a mathematical game of strategy in which two players take turns removing objects from a pile. On each turn, a player must remove at least one object, and may remove at most 3 of objects.

The version you are playing is a variant called "21". The rules are:

• A number of sticks are placed on the table.
• Players can remove 1, 2, or 3 sticks on their turn.
• The player who is forced to take the last stick loses (this is called a misère game).