#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>
#include <cstring>
#include <random>
#include <functional>
#include <numeric>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)
#define all(c) (c).begin(), (c).end()
#define zero(a) memset(a, 0, sizeof a)
#define minus(a) memset(a, -1, sizeof a)
#define minimize(a, x) a = std::min(a, x)
#define maximize(a, x) a = std::max(a, x)

using ll  = long long;
int const inf = 1<<29;

int N;
double dp[114514];

double yajue(double x) {
  REP(i, 1, N+1) {
    dp[i] = 0;
    REP(j, 1, 7) {
      if(i < j) {
        dp[i] += x;
      }
      else {
        dp[i] += dp[i-j];
      }
    }
    dp[i] = 1 + dp[i] / 6.0;
  }
  return dp[N];
}

int main() {


  cin >> N;
  double l = 0, r = 114514810;
  rep(i, 893) {
    double m = (l + r) / 2.0;
    if(m <= yajue(m)) {
      l = m;
    }
    else {
      r = m;
    }
  }

  printf("%.10f\n", l);

  return 0;
}