#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  double x, y, avg = 0;
  for (int i = 0; i < n; ++i) {
    cin >> x >> y;
    avg += y;
  }
  avg /= n;
  avg += 5;
  cout << setprecision(3) << fixed << avg << endl;
  return 0;
}
