Aerith and Bob take turns picking a nonnegative integer, each time subtracting a (positive) divisor from the other's last number. The first person to pick 0 loses. For example, if Aerith reached 2020 on some turn, Bob could pick $2020-20=2000$, as 20 is a divisor of 2020.

Continuing this example (with Aerith now picking a divisor of 2000), if both of them play optimally, who wins?
If $1998=2000-2$ were a losing position, Aerith would pick it. Otherwise, she can choose $1999=2000-1$. and since this is prime, Bob must pick either $1999-1999-0$ or $1999-1=1998$. In any case, Aerith wins.