#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = (ll)(1e+9) + 7;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
typedef pair<ld, ld> LDP;
ld px[70];
ld py[70];
int main() {
	px[0] = py[0] = 1;
	int n, l; cin >> n >> l;
	rep(i, n) {
		per(j, 61) {
			rep1(k, 6) {
				px[j + k] += px[j] * (1 / 6.0);
			}
			px[j] = 0;
		}
		if (i < n - l) {
			per(j, 61) {
				rep1(k, 6) {
					py[j + k] += py[j] * (1 / 6.0);
				}
				py[j] = 0;
			}
		}
		else {
			per(j, 61) {
				Rep1(k,4, 6) {
					py[j + k] += py[j] * (1 / 3.0);
				}
		        py[j] = 0;
			}
		}
	}
	cout << fixed << setprecision(5);
	ld out = 0;
	rep(i, 61) {
		rep(j, i) {
			out += py[i] * px[j];
		}
	}
	cout << out << endl;
	return 0;
}