#include<bits/stdc++.h>
//#include<atcoder/all>

using namespace std;
//using namespace atcoder;
using ll = long long;
using ull = unsigned long long;
using P = pair<int,int>;
#define rep(i,n) for(ll i = 0;i < (ll)n;i++)
#define ALL(x) (x).begin(),(x).end()
#define MOD 1000000007



int main(){
  
  cout << fixed << setprecision(20);
  int k;
  cin >> k;
  if(k == 0){
    cout << acos(-1)*acos(-1)/6 << "\n";
  }else{
    double res = 0;
    for(int i = 1;i <= k;i++)res += 1.0/i;
    res /= k;
    cout << res << "\n";
  }


  return 0;
}