#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  double x, y, sum = 0;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> x >> y;
    sum += y;
  }
  sum /= n;
  printf("%.3f\n", sum + 5);
  return 0;
}
