Intro to game programming.....

Consider a game where there are two piles of pebbles. On a players turn, he may remove between 1 and 3 pebbles from the first pile or between 1 and 4 pebbles from the second pile. The person who removes the last pebble wins. Label a game of this form as (x, y) where x is the initial number of pebbles in the first pile and y is the initial number of pebbles in the second pile. How many values of (x, y) are there with x [1..20], y [1..20] that are first player wins assuming that both players play optimally.