#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
#include <cstring>
#include <deque>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
#define CLR(mat) memset(mat, 0, sizeof(mat))
typedef long long ll;
int main()
{
  int N, K; cin >> N >> K;
  double dp1[N+1][6*N+1], dp2[N+1][6*N+1];
  CLR(dp1);
  CLR(dp2);
  dp1[0][0] = dp2[0][0] = 1.0;
  // 二郎
  FOR(i,0,N) {
    FOR(j,0,6*N+1) {
      FOR(m,1,7) {
        if(j+m<=6*N)
          dp1[i+1][j+m] += dp1[i][j] / 6;
      }
    }
  }
  FOR(i,0,N) {
    FOR(j,0,6*N+1) {
      if(i+1 > K) {
        FOR(m,1,7) {
          if(j+m<=6*N)
            dp2[i+1][j+m] += dp2[i][j] / 6;
        }
      } else {
        FOR(m,4,7) {
          if(j+m<=6*N)
            dp2[i+1][j+m] += dp2[i][j] / 3;
        }
      }
    }
  }
  double ans = 0;
  FOR(i,0,6*N+1) FOR(j,0,i) ans += dp2[N][i] * dp1[N][j];
  printf("%.10lf\n", ans);
  return 0;
}