#include <bits/stdc++.h>
using namespace std;
int n;
double summ, x, y;
int main() {
  scanf("%d", &n);
  for (int i = (1); i <= (n); i++) scanf("%lf %lf", &x, &y), summ += y;
  printf("%.10lf\n", 5 + summ / n);
  return 0;
}
