#include <bits/stdc++.h>
using namespace std;
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define vv(type, c, m, n, i) vector<vector<type>> c(m, vector<type>(n, i))
#define mat(type, c, m, n) vector<vector<type>> c(m, vector<type>(n));for(auto& r:c)for(auto& i:r)cin>>i;
#define rep(i,a,n) for(int i=(a), i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,n) for(int i=(a), i##_len=(n); i>i##_len; --i)
#define each(x,y) for(auto &(x):(y))
#define var(type, ...)type __VA_ARGS__;Scan(__VA_ARGS__);
template<typename T> void Scan(T& t) { cin >> t; }
template<typename First, typename...Rest>void Scan(First& first, Rest&...rest) { cin >> first; Scan(rest...); }
#define vec(type, c, n) vector<type> c(n);for(auto& i:c) cin>>i;
#define len(x) ((int)(x).size())
#define mp make_pair
#define eb emplace_back
#define em emplace
#define pb pop_back
#define fi first
#define se second
#define get(a, i) get<i>(a)
#define bit_count __builtin_popcount
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<long long> vll;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef pair<int, int> pii;
#define mini min_element
#define maxi max_element
#define sum accumulate
#define chmax(a,b) if(a<b)a=b
#define chmin(a,b) if(a>b)a=b
template <class T> inline void print(T t){cout << t << "\n";}
template <class H, class... T> inline void print(H h, T... t){cout << h << " ";print(t...);}
#define MAX 70
ll sai[11][MAX];
ll ika[11][MAX];
ll A[MAX], B[MAX];
void f2(int n) {
	rep(i, 1, n) {
		rep(j, i * 4, i * 6 + 1) {
			rep(k, 4, 7) {
				ika[i + 1][j + k] += ika[i][j] * ika[1][k];
			}
		}
	}
}
void f(int n) {
	rep(i, 1, n) {
		rep(j, i, i * 6 + 1) {
			rep(k, 1, 7) {
				sai[i + 1][j + k] += sai[i][j] * sai[1][k];
			}
		}
	}
}
double solve() {
	var(int, n, k);
	sai[1][1] = sai[1][2] = sai[1][3] = sai[1][4] = sai[1][5] = sai[1][6] = 1;
	ika[1][4] = ika[1][5] = ika[1][6] = 2;
	f(n);
	f2(k);
	if (k == 0) {
		rrep(i, n * 6, n - 1) {
			B[i] = B[i + 1] + sai[n][i];
		}
	} else if (k == n) {
		rrep(i, n * 6, n - 1) {
			B[i] = B[i + 1] + ika[n][i];
		}
	} else {
		rep(i, n - k, (n - k) * 6 + 1) {
			rep(j, k * 4, k * 6 + 1) {
				A[i + j] += sai[n - k][i] * ika[k][j];
			}
		}
		rrep(i, n * 6, n - 1) {
			B[i] = B[i + 1] + A[i];
		}
	}
	ll cnt = 0;
	rep(i, n, n * 6 + 1) {
		cnt += sai[n][i] * B[i + 1];
	}
	return cnt / pow(6, n * 2);
}
int main() {
	cout << setprecision(12) << fixed;
	print(solve());
	return 0;
}