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