#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD 1000003
#define INF 100000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;


int main() {
	int n, k;
	cin >> n >> k;
	double dp1[101] = {};
	double dp2[101] = {};
	dp1[0] = 1; 
	dp2[0] = 1;
	REP(i, n) {
		for (int j = 60; j >= 0; --j) {
			FOR(k, 1, 7) {
				dp1[j + k] += dp1[j] / 6;
			}
			dp1[j] = 0;
		}
	}
	REP(i, k) {
		for (int j = 60; j >= 0; --j) {
			FOR(k, 4, 7) {
				dp2[j + k] += dp2[j] / 3;
			}
			dp2[j] = 0;
		}
	}
	REP(i, n - k) {
		for (int j = 60; j >= 0; --j) {
			FOR(k, 1, 7) {
				dp2[j + k] += dp2[j] / 6;
			}
			dp2[j] = 0;
		}
	}
	double ans = 0;
	REP(i, 100) {
		REP(j, i) {
			ans += dp1[j] * dp2[i];
		}
	}
	cout << setprecision(6) << fixed << ans << endl;
	return 0;
}