#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N,K;
    cin >> N >> K;
    double dp1[N+1][70],dp2[N+1][70];
    rep(i,0,N+1)rep(j,0,61)dp1[i][j] = dp2[i][j] = 0;
    dp1[0][0] = 1;
    dp2[0][0] = 1;
    rep(i,0,N)rep(j,0,60)rep(k,1,7){
        dp1[i+1][j + k] += dp1[i][j] / 6;
    }
    rep(i,0,61)dp2[N-K][i] = dp1[N-K][i];
    rep(i,N-K,N+K)rep(j,0,60)rep(k,4,7){
        dp2[i+1][j + k] += dp2[i][j] / 3;
    }
    double ans = 0;
    rep(i,0,61)rep(j,i+1,61){
        ans += dp2[N][j] * dp1[N][i];
    }
    cout << ans << endl;
}