#include <iostream>
using namespace std;
#include <cstdio>
#include <string.h>
#include <stdlib.h>
#include <math.h>

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;
typedef unsigned long long ull;
typedef long double lb;

/* ここからが本編 */
int main(void)
{
   int i,j,k;
   int n;
   double e[30]={0},*dp;
   dp = e + 6; 
   REP(i,-6,1) dp[i] = 0;
   REP(i,1,21) {
      dp[i] = 1;
      rep(j,6) dp[i] += dp[i-6+j]/6;
   }
   cin >> n;
   printf("%.14g\n",dp[n]);
   return 0;
}