#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

const int N=1010;
double a[N][N],f[N];
int n,m,st,ed;

void solve(){
  for(int k=n-1; k>=st; k--){
    memset(a,0,sizeof a);
    for(int i=1; i<=m; i++){
      if(i==1){
        a[i][i]=2;
        a[i][i+1]=-1;
        a[i][m+1]=3+f[i];
        continue;
      } 
      else if(i==m){
        a[i][i]=2;
        a[i][i-1]=-1;
        a[i][m+1]=3+f[i];
        continue;
      }
      a[i][i]=3;
      a[i][i+1]=-1;
      a[i][i-1]=-1;
      a[i][m+1]=4+f[i];
    }
    
    for(int i=1; i<m; i++){
      double p=a[i+1][i]/a[i][i];
      a[i+1][i]=0;
      a[i+1][i+1]-=a[i][i+1]*p;
      a[i+1][m+1]-=a[i][m+1]*p;
    }
    f[m]=a[m][m+1]/a[m][m];
    for(int i=m-1; i>=1; i--)
      f[i]=(a[i][m+1]-f[i+1]*a[i][i+1])/a[i][i];
  }
}
int main(){
  scanf("%d %d",&n,&m);
  scanf("%d %d",&st,&ed);
  if(m==1){
    printf("%.10f\n",2.0*(n-st)); return 0;
  }
  solve();
  printf("%.10f\n",f[ed]);
}