#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-12;

int main() {
	int n, k;
	cin >> n >> k;
	
	int v[2][6] = {{1,2,3,4,5,6},{4,4,5,5,6,6}};
	
	double dp[11][61] = {};
	dp[0][0] = 1.0;
	
	REP(i, n) {
		int p;
		if (i < n - k) p = 0;
		else p = 1;
		
		REP(j, 61) REP(k, 6) if (j + v[p][k] <= 60) dp[i + 1][j + v[p][k]] += dp[i][j] / 6.0;
	}
	
	int cnt[11][61] = {};
	cnt[0][0] = 1;
	REP(i, n) REP(j, 61) REP(k, 6) if (j + v[0][k] <= 60) cnt[i + 1][j + v[0][k]] += cnt[i][j];
	
	double ans = 0;
	REP(i, 61) {
		if (cnt[n][i] == 0) continue;
		double now = 0;
		FOR(j, i + 1, 61) now += dp[n][j];
		now *= cnt[n][i];
		
		ans += now;
	}
	ans /= pow(6, n);
	
	printf("%.15f\n", ans);
	
	return 0;
}