#include <iostream>
#include <algorithm>
#include <cstdio>
#include <string>
#include <vector>
#include <numeric>

#define ll long long

using namespace std;

ll T[61];
ll J[61];

//再帰なし累乗
ll pow(int x, int p){
  ll result;
	for(result=1;p!=0;p>>=1)
	{
    if(p&1) result*=x;
	  x*=x;
  }
  return result;
}

int main(){
  
   int n,k;
   cin>>n>>k;
   ll po=pow(6,n);
   for(ll i=0;i<po;++i){
     ll t=i;
     ll sumt=0,sumj=0;
     for(int j=0;j<n;++j){
         sumj+=t%6+1;
         if(j<k){
             sumt+=t%3+4;
         }else{
             sumt+=t%6+1;
         }
         t/=6;
     }
     T[sumt]++;
     J[sumj]++;  
   }

   ll all=po*po;
   ll frac=0;
   ll rest=0;
   for(int i=1;i<=6*n;++i){
       ll sum=0;
       for(int j=1;j<i;++j) sum+=J[j];
       frac+=(T[i]*sum);
   }

   printf("%.5lf\n",(double)frac/all);

   return 0;
}