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

#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef pair<int, int> P;
typedef unsigned int uint;
typedef unsigned long long ull;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};

const int inf = 1000000009;
const double eps = 1e-8;

double solve(int n, int k) {
    int tarou[n+1][6*n+1], jirou[n+1][6*n+1];
    memset(tarou, 0, sizeof(tarou));
    memset(jirou, 0, sizeof(jirou));

    tarou[0][0] = jirou[0][0] = 1;
    for (int i = 0; i < n; i++) {
	for (int j = 0; j <= 6*n; j++) {
	    for (int k = 1; k <= 6; k++) {
		if (j + k <= 6 * n)
		    jirou[i+1][j+k] += jirou[i][j];
	    }
	}
    }


    for (int i = 0; i < n-k; i++) {
	for (int j = 0; j <= 6*n; j++) {
	    for (int k = 1; k <= 6; k++) {
		if (j + k <= 6 * n)
		    tarou[i+1][j+k] += tarou[i][j];
	    }
	}
    }
    int spe[6] = {4, 4, 5, 5, 6, 6};
    for (int i = n-k; i < n; i++) {
	for (int j = 0; j <= 6*n; j++) {
	    for (int k = 0; k < 6; k++) {
		if (j + spe[k] <= 6 * n)
		    tarou[i+1][j+spe[k]] += tarou[i][j];
	    }
	}
    }
    /*
    for (int i = 1; i <= 6 * n; i++) {
	cout << i << ": " << jirou[i] << " " << tarou[i] << endl;
    }
    */
    int sumj, sumt = 0;
    for (int i = 1; i <= 6 * n; i++) {
	sumt += tarou[n][i];
	jirou[n][i] += jirou[n][i-1];
    }
    sumj = jirou[n][6*n];

    double res = 0;
    for (int i = 1; i <= 6 * n; i++) {
	res += (double)tarou[n][i] / sumt * jirou[n][i-1] / sumj;
    }
    
    return res;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    int n, k;
    cin >> n >> k;
    cout << solve(n, k) << endl;
}