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