#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=(r)-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={1,0,-1,0,1,1,-1,-1,0};
const ll dx[9]={0,-1,0,1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

int main(){
    vector<vector<double>> dp(20,vector<double>(100)),ndp=dp;
    ll n,L;cin >> n >>L;
    dp[0][0]=1;ndp[0][0]=1;
    rep(i,n){
        rep(j,90){
            rep(k,6){
                dp[i+1][j+k+1]+=dp[i][j]/6;
            }
        }
    }
    rep(i,n){
        rep(j,90){
            if(i>=n-L){
                rep(k,3){
                    ndp[i+1][j+k+4]+=ndp[i][j]/3;
                }
                continue;
            }
            rep(k,6){
                ndp[i+1][j+k+1]+=ndp[i][j]/6;
            }
        }
    }
    /*rep(i,n+1){
        rep(j,30)cout << ndp[i][j] <<" ";cout << endl;
    }*/
    double ans=0;
    rep(i,100){
        rep(j,i)ans+=ndp[n][i]*dp[n][j];
    }
    CST(10);
    cout << ans <<endl;
}