#include <bits/stdc++.h>
using namespace std;
int main() {
  double y, ans = 0;
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> y;
    cin >> y;
    ans += y;
  }
  printf("%.3lf", ans / (1.00 * n) + 5);
}
