#include<iostream>
using namespace std;
const int N = 25;
const int M = 25;
long long  MAP[N][M];
int  n, m;
int x_b, y_b;
int x_c, y_c;

bool pd(int x, int  y)
{
    if (abs(x_c - x) == 1 && abs(y_c - y) == 2)
    {
        return 1;
    }
    else if (abs(x_c - x) == 2 && abs(y_c - y) == 1)
    {
        return 1;
    }
    else if(x_c-x==0 && y_c-y==0)
    {
        return 1;
    }
    else {
        return 0;
    }
}


int main()
{
    cin >> x_b >> y_b >> x_c >> y_c;
    for (int i = 0; i <= x_b; i++)
    {
        if (pd(i, 0))
        {
            MAP[i][0] = 0;
        }
        else {
            MAP[i][0] = 1;
        }
    }
    for (int j = 0; j <= y_b; j++)
    {
        if (pd(0, j))
        {
            MAP[0][j] = 0;
        }
        else {
            MAP[0][j] = 1;
        }
    }



    for (int i = 1; i <= x_b; i++)
    {
        for (int j = 1; j <= y_b; j++)
        {
            if (pd(i, j))
            {
                MAP[i][j] = 0;
            }
            else {
                MAP[i][j] = MAP[i - 1][j] + MAP[i][j - 1];
            }
        }
    }
    cout << MAP[x_b][y_b];

    return 0;
}