#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)

int main(){
  double k;
  cin>>k;
  if(k==0){
    cout<<fixed<<setprecision(12)<<(M_PI*M_PI)/6<<endl;
    return 0;
  }
  double sum=0;
  for (int i=1;i<=k;i++)sum+=(double)1/i;
  double ans=(1/k)*sum;
  cout<<fixed<<setprecision(12)<<ans<<endl;
  return 0;
}