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