#include<stdio.h>
#include<string.h>
#define max(a,b) (a>b?a:b)
#define N 1100

int dp[N][N];

int main()
{
    int n, P, M, T;

    while(scanf("%d%d%d%d", &n, &P, &M, &T)!=EOF)
    {
        int i, j;

        memset(dp, 0, sizeof(dp));

        dp[0][P] = 1;

        for(i=1; i<=M; i++)
        for(j=1; j<=n; j++)
        {
            dp[i][j] = dp[i-1][j-1] + dp[i-1][j+1];
        }

        printf("%d\n", dp[M][T]);
    }
    return 0;
}