Question 115
100 thimbles are arranged on a circle. A token is placed under one of the thimbles. By one turn, a player can pick up arbitrary four thimbles and check whether a token is under one of them. After that, the thimbles return to their places, and the token moves to one of the two neighboring thimbles. Find the least number of turns needed to find the token for sure. (B. Trushin)