#define _CRT_SECURE_NO_WARNINGS
#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<random>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())


int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	int n,k;
	cin>>n>>k;
	double p1[61]={},p2[61]={};
	p1[0]=p2[0]=1;
	rep(j,n){
		for(int i=(n-1)*6;i>=0;i--){
			rep(d,6){
				p1[i+d+1]+=p1[i]/6;
			}
			p1[i]=0;
		}
	}
	rep(j,k){
		for(int i=(n-1)*6;i>=0;i--){
			rep(d,3){
				p2[i+d+4]+=p2[i]/3;
			}
			p2[i]=0;
		}
	}
	rep(j,n-k){
		for(int i=(n-1)*6;i>=0;i--){
			rep(d,6){
				p2[i+d+1]+=p2[i]/6;
			}
			p2[i]=0;
		}
	}
	double ans=0;
	double s=0;
	for(int i=1;i<=n*6;i++){
		ans += p2[i]*s;
		s+=p1[i];
	}
	printf("%.3f\n",ans);
	return 0;
}