#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double sum = 0.0;
  for (int i = 1; i <= n; i++) {
    double x, y;
    cin >> x >> y;
    sum += y;
  }
  printf("%.3f\n", double(sum / n) + 5.0);
  return 0;
}
