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