#include <iostream>
using namespace std;

int main() {
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    long long f[21][21] = {0};
    f[0][0] = 1;
    for (int i = 0; i <= n; i++) {
        for (int j = 0; j <= m; j++) {
            if (i == 0 && j == 0) continue;
            if (i == x && j == y) {
                f[i][j] = 0;
                continue;
            }
            if (i > x && j > y) {
                f[i][j] = f[i - 1][j] + f[i][j - 1];
            } else if (i > x) {
                f[i][j] = f[i - 1][j];
            } else if (j > y) {
                f[i][j] = f[i][j - 1];
            }
        }
    }
    cout << f[n][m] << endl;
    return 0;
}