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