int F(int n, int x, int y) {
if (n == 0) {
return x + y;
} else if (y == 0) {
return x;
}
return F(n - 1, F(n, x, y - 1), F(n, x, y - 1) + y);
void main() {
print('F(1,3,3) = ${F(1, 3, 3)}');