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