#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std; // NOLINT

void dfs(int32_t sum, int32_t c, unordered_map<int32_t, int32_t> &hist) {
    if (c == 0) {
        ++hist[sum];
        return;
    }
    for (auto i = 1; i <= 6; ++i) {
        dfs(sum + i, c - 1, hist);
    }
}

void dfs2(int32_t sum, int32_t c, int32_t d,
          unordered_map<int32_t, int32_t> &hist) {
    if (c == 0) {
        dfs(sum, d, hist);
        return;
    }
    for (auto i = 4; i <= 6; ++i) {
        dfs2(sum + i, c - 1, d, hist);
        dfs2(sum + i, c - 1, d, hist);
    }
}

int main() {
    int32_t n, k;
    cin >> n >> k;
    unordered_map<int32_t, int32_t> hist1, hist2;
    dfs(0, n, hist1);
    dfs2(0, k, n - k, hist2);
    int64_t sum = 0, win = 0;
    for (auto [k2, v2] : hist2) {
        for (auto [k1, v1] : hist1) {
            sum += int64_t(v1) * v2;
            if (k2 > k1)
                win += int64_t(v1) * v2;
        }
    }
    printf("%.6f\n", double(win) / sum);
    return 0;
}