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

#define lp(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) lp(i, 0, n)
#define rlp(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); i--)
#define rrep(i, n) rlp(i, 0, n)

#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define all(c) begin(c), end(c)

typedef long long ll;
typedef unsigned long long ull;

template<typename T>
inline bool chmin(T &a, T b){
	if (a <= b) return false;
	a = b; return true;
}

template<typename T>
inline bool chmax(T &a, T b){
	if (a >= b) return false;
	a = b; return true;
}

template<typename T>
inline void unique(T &c){
	sort(all(c));
	c.erase(unique(all(c)), end(c));
}

template<typename T>
inline T sq(T a){
	return a * a;
}

int n, k;
double dp[10][100][100];

double calc(int i, int a, int b)
{
	if (i == n) return a > b ? 1 : 0;
	if (dp[i][a][b] != -1.0) return dp[i][a][b];
	double res = 0;
	if (i < k){
		lp(i1, 4, 7) lp(i2, 1, 7){
			res += 2 * calc(i + 1, a + i1, b + i2);
		}
	}
	else {
		lp(i1, 1, 7) lp(i2, 1, 7){
			res += calc(i + 1, a + i1, b + i2);
		}
	}
	return dp[i][a][b] = res / 36;
}

int main()
{
	cin >> n >> k;
	fill_n(**dp, 100000, -1);
	double res = calc(0, 0, 0);
	printf("%.20f\n", res);
}