#include <bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
signed main(){
  int N;
  cin>>N;
  double ans = 0;
  for(int i=1;i<1000000;i++) ans += 1.0/(i*(i+N));
  cout<<fixed<<setprecision(12);
  cout<<ans+0.0000001<<endl;
}