#include <bits/stdc++.h>
using namespace std;
int main() {
  double ans = 0;
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    double x, y;
    scanf("%lf%lf", &x, &y);
    ans += y;
  }
  printf("%.3lf\n", ans / n + 5.0);
  return 0;
}
