#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double sum = 0, t;
  for (int i = 1; i <= n; i++) {
    scanf("%*lf%lf", &t);
    sum += t;
  }
  cout << sum / n + 5;
  return 0;
}
