#include <bits/stdc++.h>
using namespace std;

using ld=long double;
ld dp[30];

ld f(int n,int k){
  if(dp[n]>=0)return dp[n];
  if(n>=k)return 0;
  ld res=1;
  for(int i=0;i<6;i++)res+=f(n+i+1,k)/6;
  return dp[n]=res;
}


signed main(){
  for(int i=0;i<30;i++)dp[i]=-1;
  int k;cin>>k;
  cout<<fixed<<setprecision(12)<<f(0,k)<<endl;
}