#include <bits/stdc++.h>
using namespace std;
double x, y, ans = 0;
int n;
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> x >> y;
    ans += y;
  }
  ans = ans / n;
  ans += 5;
  cout << fixed << setprecision(3) << ans;
  return 0;
}
