#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

ll dp1[15][100];
ll dp2[15][100];

int main(){
  int N, K;
  cin >> N;
  cin >> K;

  ll ret1 = 0, ret2 = 0;
  
  vector<int> sai1, sai2;
  sai1.push_back(1);
  sai1.push_back(2);
  sai1.push_back(3);
  sai1.push_back(4);
  sai1.push_back(5);
  sai1.push_back(6);

  sai2.push_back(4);
  sai2.push_back(4);
  sai2.push_back(5);
  sai2.push_back(5);
  sai2.push_back(6);
  sai2.push_back(6);

  dp1[0][0] = 1;
  rep(i,N){
    rep(j,100){
      rep(k,sai1.size()){
        dp1[i+1][j+sai1[k]] += dp1[i][j];
      }
    }
  }
  
  dp2[0][0] = 1;
  rep(i,N){
    rep(j,100){
      if(i<K){
        rep(k,sai2.size()){
          dp2[i+1][j+sai2[k]] += dp2[i][j];
        }
      }else{
        rep(k,sai1.size()){
          dp2[i+1][j+sai1[k]] += dp2[i][j];
        }
      }
    }
  }

  rep(i,100){
    rep(j,i){
      ret2 += dp1[N][j] * dp2[N][i];
      ret1 += dp1[N][j] * dp2[N][i];
    }
    REP(j,i,100){
      ret1 += dp1[N][j] * dp2[N][i];
    }
  }

  printf("%.9lf\n", ret2/(double)ret1);
  return 0;
}