#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<ctime>
using namespace std;

#define rrep(i, m, n) for(int i=m; i<n; i++)
#define erep(i, m, n) for(int i=m; i<=n; i++)
#define  rep(i, n)    for(int i=0; i<n; i++)

#define CNT 1E6

int k;
double res;

int main()
{
  cin >> k;

  srand((unsigned)time(NULL));

  rep(j, CNT){
    int sum = 0;
    rep(i, CNT){
      sum += rand()%6+1;
      if(sum == k){
        res += i+1;
        break;
      }
      if(sum > k) sum = 0;
    }
  }

  printf("%.10f\n", res/CNT);

  return 0;
}