#include<bits/stdc++.h>

using namespace std;
typedef unsigned int uint;
typedef long long int ll;
typedef unsigned long long int ull;

#define debugv(v) printf("L%d %s => ",__LINE__,#v);for(auto e:v){cout<<e<<" ";}cout<<endl;
#define debugm(m) printf("L%d %s is..\n",__LINE__,#m);for(auto v:m){for(auto e:v){cout<<e<<" ";}cout<<endl;}
#define debuga(m,w) printf("L%d %s is => ",__LINE__,#m);for(int x=0;x<(w);x++){cout<<(m)[x]<<" ";}cout<<endl;
#define debugaa(m,w,h) printf("L%d %s is..\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){cout<<(m)[x][y]<<" ";}cout<<endl;}
#define debugaar(m,w,h) printf("L%d %s is..\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){cout<<(m)[y][x]<<" ";}cout<<endl;}
#define ALL(v) (v).begin(),(v).end()
#define BIGINT 0x7FFFFFFF
#define E107 1000000007ll
void printbit(int u){if(u==0)cout<<0;else{int s=0,k=0;for(;0<u;u>>=1,k++)s=(s<<1)|(u&1);for(;0<k--;s>>=1)cout<<(s&1);}}

#define TIME chrono::system_clock::now()
#define MILLISEC(t) (chrono::duration_cast<chrono::milliseconds>(t).count())

namespace{
    std::chrono::system_clock::time_point t;
    void tic(){t=TIME;}
    void toc(){fprintf(stderr,"TIME : %lldms\n",MILLISEC(TIME-t));}
}

template<typename T1,typename T2>
ostream& operator <<(ostream &o,const pair<T1,T2> p){o<<"("<<p.first<<":"<<p.second<<")";return o;}
template<typename T1,typename T2>
pair<T1,T2>& operator+=(pair<T1,T2>& p1,const pair<T1,T2>& p2){p1.first+=p2.first;p1.second+=p2.second;return p1;}

int width,height;
int m,n,kei;

pair<ll,ll> dfs(int index=0,int taro=0,int jiro=0){
    static map<int,pair<ll,ll>> memo;
    int key = (index<<16)|(taro<<8)|(jiro);
    if (n<=index){
        return make_pair(jiro<taro,1);
    }
    if (memo.count(key)) return memo[key];
    
    pair<ll,ll> p = make_pair(0,0);
    for (int j=1;j<=6;++j){
        for (int t=index<kei?4:1;t<=6;++t){
            p+=dfs(index+1,taro+t,jiro+j);
        }
    }
    return memo[key]=p;
}

int main(){
    int i,j,k;
    int x,y,a,b;
    
    cin >> n >> kei;
    
    pair<ll,ll> result = dfs();
    
    printf("%.10f\n",((double)(result.first)/(double)(result.second)) );
    return 0;
}