#include <bits/stdc++.h>
using namespace std;
#define int long long

int n;
int m;
int rn;
int rm;
int ans;
array <array <int, 30>, 30> a;

inline void init()
{
    scanf("%d%d", &rn, &rm);
    scanf("%d%d", &n, &m);
    rn += 3;
    rm += 3;
    n += 3;
    m += 3;
    for (int i = 3; i <= rn; i++)
    {
        for (int j = 3; j <= rm; j++)
        {
            a[i][j] = 1;
        }
    }
    a[n][m] = -1;
    a[n-1][m+2] = -1;
    a[n+1][m+2] = -1;
    a[n-1][m-2] = -1;
    a[n+1][m-2] = -1;
    a[n+2][m+1] = -1;
    a[n-2][m+1] = -1;
    a[n+2][m-1] = -1;
    a[n-2][m-1] = -1;
}

signed main(signed argc, char **argv)
{
    init();
    for (int i = 3; i <= rn; i++)
    {
        for (int j = 3; j <= rm; j++)
        {
            if (i == 3 && j == 3)
            {
                continue;
            }
            if (a[i][j] == -1)
            {
                continue;
            }
            if (a[i][j-1] == -1 && a[i-1][j] == -1)
            {
                a[i][j] = -1;
                continue;
            }
            if (a[i][j-1] != -1 && a[i-1][j] == -1)
            {
                a[i][j] = a[i][j-1];
                continue;
            }
            if (a[i][j-1] == -1 && a[i-1][j] != -1)
            {
                a[i][j] = a[i-1][j];
                continue;
            }
            a[i][j] = a[i-1][j] + a[i][j-1];
        }
    }
    printf("%d", a[rn][rm]);
    return 0;
}