Obviously, the process is finite. Claim 1 If a player gets a position with one number odd and another even, he wins If the even number is zero, remove all marbles from the odd one and win. Otherwise, take one marble from the even box. The opposite player must take an odd amount of marbles, hence we once again get the position with even and odd. It continues until the even number becomes zero, so we win. Claim 2 If a player gets a position with two odd numbers, he loses. He must take an odd amount of balls and give odd-even position for the opponent. Thus we are done by first claim. Now both players must move such that the position remains even-even, so we can divide everything by $2$. Then we have $997$ and $1012$ marbles, where first wins. Hence, Spiro wins.