#include <iostream>
using namespace std;

long long map[22][22];

int main() {
        int i, x, y, hx, hy, n[9][2] = {{0,0},{1,2},{1,-2},{2,1},{2,-1},{-1,2},{-1,-2},{-2,1},{-2,-1}};//马和可移动的8个位置
        long long  xcount, ycount;
        cin >> x >> y >> hx >> hy;
        map[1][1] = 1;
        hx++, hy++;
        x++, y++;

        //标记不可以经过的点
        int tmpx,tmpy;
        for(i = 0; i < 9; i++) {
                tmpx = hx+n[i][0];
                tmpy = hy+n[i][1];
                if(tmpx>=1&&tmpx<=21 && tmpy>=1&&tmpy<=21) map[tmpx][tmpy] = -1;
        }

        //开始走
        for(i = 1; i <= x; i++) {
                for(int j = 1; j <= y; j++) {
                        if(map[i][j] != -1) {
                                xcount = map[i-1][j];
                                ycount = map[i][j-1];
                                if(xcount > 0) map[i][j] += xcount;
                                if(ycount > 0) map[i][j] += ycount;
                        }
                }
        }
        cout << map[x][y] << endl;
        return 0;
}