#include <bits/stdc++.h>
int main() {
  int n;
  double s = 0.0, a;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%*lf%lf", &a);
    s += a;
  }
  printf("%.3f", s / n + 5.0);
  return 0;
}
