#include <bits/stdc++.h>
using namespace std;
#include <math.h>
#include <iomanip>
#include <cstdint>
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
#define rep(i,n) for (int i = 0; i < (n); ++i)
typedef long long ll;
using P = pair<int,int>;
const int INF=1001001001;
const int mod =1e9+7;

int main() {
  double k;
  cin>>k;
  if(k==0){cout<<fixed<<setprecision(10)<<M_PI*M_PI/6<<endl;return 0;}
  double sum=0;
  for(double i=1;i<=k;i++){
    double s=(double)1/i;
    sum+=s;
  }
  cout<<fixed<<setprecision(10)<<sum/k<<endl;
  return 0;
}