#include <bits/stdc++.h>
using namespace std;
int N, arr[50];
int main() {
  double avg = 0.0;
  cin >> N;
  for (int i = 0; i < N; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + N);
  for (int i = 0; i < N; i += 2) {
    avg = (arr[i] + arr[i + 1]) / 2.0;
  }
  cout << avg;
  return 0;
}
