Problem

Source: 42nd International Tournament of Towns, Senior A-Level P4, Spring 2021

Tags: combinatorics, game, Tournament of Towns



There is a row of $100N$ sandwiches with ham. A boy and his cat play a game. In one action the boy eats the first sandwich from any end of the row. In one action the cat either eats the ham from one sandwich or does nothing. The boy performs 100 actions in each of his turns, and the cat makes only 1 action each turn; the boy starts first. The boy wins if the last sandwich he eats contains ham. Is it true that he can win for any positive integer $N{}$ no matter how the cat plays? Ivan Mitrofanov