#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


struct Precision{
  Precision(){
    cout<<fixed<<setprecision(12);
  }
}precision_beet;

//INSERT ABOVE HERE
signed main(){
  int n;
  cin>>n;

  auto check=
    [&](double x){
      vector<double> dp(n+1,0);
      dp[n]=x;
      dp[0]=0;
      for(int i=1;i<=n;i++){
        dp[i]=1;
        for(int j=1;j<=6;j++)
          dp[i]+=(i-j<0?x:dp[i-j])/6;
      }
      return dp[n]>=x;
    };
    
  double l=0,r=1e9;
  for(int k=0;k<200;k++){
    double m=(l+r)/2;
    if(check(m)) l=m;
    else r=m;
  }
  cout<<l<<endl;
  return 0;
}