#include <bits/stdc++.h>
using namespace std;

int main() {
  int N; cin >> N;

  double c = 1.0 / (exp(1.0) * M_PI * M_PI);
  double ans = c * (exp(1.0) + 4*exp(cos(c / (2*N))) + exp(cos(c / N))) / 6.0;
  cout << ans << endl;

}