#include <bits/stdc++.h>
double x, y, sum;
int n;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%lf", &x, &y);
    sum += y;
  }
  printf("%.3lf", sum / n + 5);
  return 0;
}
