// No.58 イカサマなサイコロ
#include <iostream>
#include <vector>
#include <iomanip>
using namespace std;

int main(void) {
    int N, K;
    cin >> N >> K;
    int M = 6 * N;
    vector<double> dp1(M + 1), dp2(M + 1);
    dp1[0] = dp2[0] = 1;
    for (int i = 0; i < N; ++i) {
        for (int j = M; j >= 0; --j) {
            for (int k  = 1; k <= 6; ++k) {
                if (j + k > M) continue;
                dp1[j + k] += dp1[j] / 6;
            }
            dp1[j] = 0;
        }
    }
    for (int i = 0; i < K; ++i) {
        for (int j = M; j >= 0; --j) {
            for (int k = 4; k <= 6; ++k) {
                if (j + k > M) continue;
                dp2[j + k] += dp2[j] / 3;
            }
            dp2[j] = 0;
        }
    }
    for (int i = K; i < N; ++i) {
        for (int j = M; j >= 0; --j) {
            for (int k = 1; k <= 6; ++k) {
                if (j + k > M) continue;
                dp2[j + k] += dp2[j] / 6;
            }
            dp2[j] = 0;
        }
    }
    double res = 0;
    for (int i = 0; i <= M; ++i) {
        for (int j = i + 1; j <= M; ++j) {
            res += dp1[i] * dp2[j];
        }
    }
    cout << fixed << setprecision(10) << res << endl;
}