**C. 1304.** Two players are playing the following game: They take turns in writing a natural number 1 to 10 on a blackboard. It is only allowed to write a number that does not divide any of the numbers written on the board previously. If a player is not able to write a new number on the board, he loses the game. Show that the starting player has a winning strategy.

(5 points)

**Deadline expired on 12 October 2015.**