/* -*- coding: utf-8 -*-
 *
 * 58.cc: No.58 イカサマなサイコロ - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 10;

/* typedef */

typedef vector<int> vi;

/* global variables */

/* subroutines */

int roll_dice(int n, int k, vi &cs) {
  cs.assign(n * 6 + 1, 0);
  vi ds(n);
  for (int i = 0; i < k; i++) ds[i] = 4;
  for (int i = k; i < n; i++) ds[i] = 1;
  int total = 0;

  for (;;) {
    int sum = 0;
    for (int i = 0; i < n; i++) sum += ds[i];
    cs[sum]++;
    total++;

    int i = 0;
    for (; i < n; i++) {
      if (++ds[i] <= 6) break;
      ds[i] = (i < k) ? 4 : 1;
    }
    if (i >= n) break;
  }

  return total;
}

/* main */

int main() {
  int n, k;
  cin >> n >> k;

  vi cs0, cs1;

  int t0 = roll_dice(n, k, cs0);
  int t1 = roll_dice(n, 0, cs1);
  //printf("%d\n", t0);
  //for (int i = 0; i < cs0.size(); i++) printf("%d ", cs0[i]); putchar('\n');

  double p = 0.0;

  for (int i0 = 1; i0 < cs0.size(); i0++)
    for (int i1 = 0; i1 < i0; i1++)
      p += ((double)cs0[i0] / t0) * ((double)cs1[i1] / t1);

  printf("%.5lf\n", p);
  return 0;
}