#include <bits/stdc++.h>
using namespace std;
const int NUM = 1005;
double dp[NUM][NUM];
int main() {
  int n, m, a, b;
  cin >> n >> m >> a >> b;
  memset(dp, 0, sizeof(dp));
  for (int i = a + 1; i <= n; i++) {
    for (int t = 1; t <= 100; t++) {
      for (int j = 1; j <= m; j++) {
        double tmp = 2;
        if (j > 1) tmp++;
        if (j < m) tmp++;
        dp[i][j] =
            (dp[i][j + 1] + dp[i][j] + dp[i - 1][j] + dp[i][j - 1]) / tmp + 1;
      }
    }
  }
  printf("%.10lf", dp[n][b]);
}
