#include <ios>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <numeric>
#include <utility>
#include <tuple>

#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
using namespace std;
using ll = long long int;
using P = pair<ll, ll>;

// clang-format off
#ifdef _DEBUG_
#define dump(...) do{ cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; PPPPP(__VA_ARGS__); cerr << endl; } while(false)
template<typename T> void PPPPP(T t) { cerr << t; }
template<typename T, typename... S> void PPPPP(T t, S... s) { cerr << t << ", "; PPPPP(s...); }
#else
#define dump(...) do{ } while(false)
#endif
template<typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template<typename T> bool chmin(T &a, T b) { if (a > b) {a = b; return true; } return false; }
template<typename T> bool chmax(T &a, T b) { if (a < b) {a = b; return true; } return false; }
template<typename T> void print(T a) { cout << a << '\n'; }
template<typename T, typename... Ts> void print(T a, Ts... ts) { cout << a << ' '; print(ts...); }
template<typename T> istream &operator,(istream &in, T &t) { return in >> t; }
// clang-format on

#include <iomanip>

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n, k;
    cin, n, k;
    auto calc = [&](int t) {
        vector<int> dp(6 * n + 1, 0);
        dp[0] = 1;
        rep(i, 0, n - t) {
            vector<int> dp2(6 * n + 1, 0);
            rep(j, 0, 6 * n + 1) {
                rep(w, 1, 7) {
                    dp2[j + w] += dp[j];
                }
            }
            dp = move(dp2);
        }
        rep(i, 0, t) {
            vector<int> dp2(6 * n + 1, 0);
            rep(j, 0, 6 * n + 1) {
                rep(w, 4, 7) {
                    dp2[j + w] += 2 * dp[j];
                }
            }
            dp = move(dp2);
        }
        return dp;
    };
    auto res1 = calc(0), res2 = calc(k);
    ll sum1 = accumulate(res1.begin(), res1.end(), 0LL);
    ll sum2 = accumulate(res2.begin(), res2.end(), 0LL);
    ll sum = 0;
    double ans = 0.0;
    rep(i, 1, 6 * n + 1) {
        sum += res2[i];
        ans += (double(res1[i]) / sum1) * (double(sum) / sum2);
    }

    cout << fixed << setprecision(15) << 1 - ans << endl;

    return 0;
}