#include <bits/stdc++.h>
int main() {
  int i, n;
  double a, b, ans = 0;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) scanf("%lf %lf", &a, &b), ans += b;
  printf("%3lf", ans / n + 5);
  return 0;
}
