#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  double x, y, ans = 0.0;
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) scanf("%lf%lf", &x, &y), ans += y;
  printf("%.3lf", ans / n + 5);
  return 0;
}
