#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a; i < n; i++)
#define per(i,n,a) for (int i = n - 1; i >= a; i--)
using namespace std;
#define MAX 100

double dp1[MAX],dp2[MAX];
int main() {
    int N, K;
    cin >> N >> K;
    dp1[0] = dp2[0] = 1;
    for (int i = 0; i < N; i++) {
        for (int j = MAX - 10; j >= 0; j--) {
            for (int k = 1; k <= 6; k++) {
                dp1[j + k] += dp1[j] / 6;
            }
            dp1[j] = 0;
        }
    }
    for (int i = 0; i < K; i++) {
        for (int j = MAX - 10; j >= 0; j--) {
            for (int k = 4; k <= 6; k++) {
                dp2[j + k] += dp2[j] / 3;
            }
            dp2[j] = 0;
        }
    }
    for (int i = K; i < N; i++) {
        for (int j = MAX - 10; j >= 0; j--) {
            for (int k = 1; k <= 6; k++) {
                dp2[j + k] += dp2[j] / 6;
            }
            dp2[j] = 0;
        }
    }
    double ans = 0;
    for (int i = 0; i < MAX; i++) {
        for (int j = i + 1; j < MAX; j++) {
            ans += dp1[i] * dp2[j];
        }
    }
    printf("%.14f\n", ans);
}