#include <bits/stdc++.h>
using namespace std;

int main() {
  double A;
  cin >> A;
  int X;
  int sum = 0;
 for(int i = 0;i < A;i++){
   cin >> X;
   sum += X;
   cin >> sum
}
 double H = sum / A;
  double C = A * A;
  cout << H / C << endl;
}
