/* -*- coding: utf-8 -*-
 *
 * 75.cc: No.75 回数の期待値の問題 - 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_K = 200;

/* typedef */

/* global variables */

double es[MAX_K + 1];

/* subroutines */

bool check(int k, double e) {
  es[k] = 0.0;
  for (int i = k - 1; i >= 0; i--) {
    double sum = 0.0;
    for (int j = 1; j <= 6; j++)
      sum += (i + j > k) ? e : es[i + j];
    es[i] = 1.0 + sum / 6;
  }

  return es[0] <= e;
}

/* main */

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

  double e0 = 0.0, e1 = 1e10;
  for (int i = 0; i < 100; i++) {
    double e = (e0 + e1) / 2;
    if (check(k, e)) e1 = e;
    else e0 = e;
  }

  printf("%.5lf\n", e1);
  return 0;
}