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