#include<bits/stdc++.h>
using namespace std;

#define int long long

typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>void chmax(T &t,U f){if(t<f)t=f;}

int N,K;

int a[100],b[100];

signed main(){
    cin>>N>>K;

    a[0]=1;b[0]=1;
    rep(i,N){
        for(int j=60;j>=0;j--){
            a[j]=0;b[j]=0;
            rep(k,6){
                int l=k+1;
                int m=k+1;
                if(i<K&&k<3)l+=3;
                if(j-l>=0)a[j]+=a[j-l];
                if(j-m>=0)b[j]+=b[j-m];
            }
        }
    }

    int ans=0;
    rep(i,60+1){
        ans+=a[i]*accumulate(b,b+i,0ll);
    }
    int d=1;
    rep(i,2*N)d*=6;
    printf("%.20lf\n",1.0*ans/d);

    return 0;
}