#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

int main(){
	
	int n,K;
	cin>>n>>K;
	
	vector<double> dp0(6*n+1,0.0);
	dp0[0] = 1.0;
	
	rep(i,n){
		vector<double> ndp(6*n+1,0.0);
		rep(j,6*n+1){
			for(int k=1;k<=6;k++){
				if(j+k<=6*n){
					ndp[j+k] += dp0[j] / 6.0;
				}
			}
		}
		swap(dp0,ndp);
	}
	
	vector<double> dp1(6*n+1,0.0);
	dp1[0] = 1.0;
	
	rep(i,n){
		vector<double> ndp(6*n+1,0.0);
		rep(j,6*n+1){
			if(i>=K){
				for(int k=1;k<=6;k++){
					if(j+k<=6*n){
						ndp[j+k] += dp1[j] / 6.0;
					}
				}
			}
			else{
				for(int k=4;k<=6;k++){
					if(j+k<=6*n){
						ndp[j+k] += dp1[j] / 3.0;
					}
				}
			}
		}
		swap(dp1,ndp);
	}
	double ans = 0.0;
	rep(i,6*n+1){
		for(int j=i+1;j<=6*n;j++){
			ans += dp0[i] * dp1[j];
		}
	}
	
	cout<<fixed<<setprecision(10)<<ans<<endl;
	
	return 0;
}