Question 191
On an $8 \times 8$-board there is a beetle on every square. At a certain moment the distribution of the beetles on the board changes: every beetle crawls either one square to the left or one square diagonally to the bottom right. If a beetle can make neither of the two movements without falling off the board, it stays on its square.
At most how many squares can end up empty by this change?
At most how many squares can end up empty by this change?