#include <bits/stdc++.h>
using namespace std;
int main() {
  double k = 0;
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    double x, y;
    cin >> x >> y;
    k += y;
  }
  printf("%.3lf", k / 1.0 / n + 5.0);
}
