#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  double a, b, m = 0;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> a >> b;
    m += b;
  }
  m /= n;
  cout << fixed << setprecision(3) << m + 5;
  return 0;
}
