1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #define MAX 105
 5 using namespace std;
 6 int dp[MAX][MAX];
 7 int main(){
 8     int n, t, m, p;
 9     /* freopen("in.c", "r", stdin); */
10     while(~scanf("%d%d%d%d", &n, &p, &m, &t)){
11         memset(dp, 0, sizeof(dp));
12         dp[1][p-1] = dp[1][p+1] = 1;
13         for(int i = 2;i <= m;i ++){
14             for(int j = 1;j <= n;j ++){
15                 if(j > 1 && j < n) dp[i][j] += dp[i-1][j+1] + dp[i-1][j-1];
16                 else if(j == 1) dp[i][j] += dp[i-1][j+1];
17                 else dp[i][j] += dp[i-1][j-1];
18             }
19         }
20         printf("%d\n", dp[m][t]);
21     }
22     return 0;
23 }