#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>
#include <random>
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;
// 二分探索var
// dp[0] = x
int K;
double dp[222];
double calc(double x) {
  CLR(dp);
  for(int i = K - 1; i >= 0; i--) {
    FOR(j,1,7) {
      if(i + j > K) dp[i] += x;
      else dp[i] += dp[i+j];
    }
    dp[i] = dp[i] / 6.0 + 1;
  }
  return dp[0];
}
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> K;
  double l = 0, r = 1e9;
  FOR(i,0,100) {
    double c = (l + r) / 2;
    if(calc(c) >= c) l = c;
    else r = c;
  }
  cout << (l + r) / 2 << endl;
}