#include <iostream>
#include <vector>
#include <iomanip>
using namespace std;
int main(){
  int n,x;cin>>n>>x;
  vector<vector<long double>> A(n+1,vector<long double>(6*n+1));
  A[0][0] = 1;
  for(int i = 0; n > i; i++){
    for(int j = 0; 6*i >= j; j++){
      for(int k = 1; 6 >= k; k++){
        A[i+1][j+k] += A[i][j]/6;
      }
    }
  }
  vector<vector<long double>> B(n+1,vector<long double>(6*n+1));
  B[0][0] = 1;
  for(int i = 0; n > i; i++){
    for(int j = 0; 6*i >= j; j++){
      for(int k = 1; 6 >= k; k++){
        if(i < x){
          if(k <= 3)continue;
          else B[i+1][j+k] += B[i][j]/3;
        }else{
          B[i+1][j+k] += B[i][j]/6;
        }
      }
    }
  }
  long double ans = 0;
  for(int i = 0; 6*n >= i; i++){
    for(int j = i+1; 6*n >= j; j++){
      ans += A[n][i]*B[n][j];
    }
  }
  cout << fixed << setprecision(10) << ans << endl;
}