#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <ctype.h>
#include <string.h>
long long dp[25][25];
int main()
{
    int x1, y1, x2, y2;
    scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
    dp[0][0] = 1;
    for (int i = 0; i <= x1; i++)
    {
        for (int j = 0; j <= y1; j++)
        {
            if (((i == x2 - 2 || i == x2 + 2) && (j == y2 - 1 || j == y2 + 1)))
                dp[i][j] = 0;
            else if (((j == y2 - 2 || j == y2 + 2) && (i == x2 - 1 || i == x2 + 1)))
                dp[i][j] = 0;
            else if (i == x2 && j == y2)
                dp[i][j] = 0;
            else if (i && j)
                dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
            else if (i)
                dp[i][j] = dp[i - 1][j];
            else if (j)
                dp[i][j] = dp[i][j - 1];
        }
    }
    printf("%d\n", dp[x1][y1]);
    system("PAUSE");
    return 0;
}