#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double sum = 0;
  double a[10000], b[10000];
  for (int i = 0; i < n; i++) {
    cin >> a[i] >> b[i];
    sum += b[i];
  }
  sum /= n;
  sum += 5;
  printf("%.3lf", sum);
  return 0;
}
