#include <bits/stdc++.h>
using namespace std;
double a, b, sum;
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a >> b;
    sum += b;
  }
  sum /= n;
  cout << sum + 5;
  return 0;
}
