There is a 9x9 board. There is a bug on each and every square. At the sound of a signal every bug moves diagonally by one square. Some squares will end up with more than one bug, and some will be empty. What is the least possible amount of empty squares?
[spoiler]I wanted to punch a kitten when I saw this on my math test. D:<[/spoiler]
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Necro ( ͡° ͜ʖ ͡°)