#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; i++) {
    cin >> v.at(i);
  }
  sort(v.begin(), v.end());
  double a, val;
  for (int i = 0; i < n - 1; i++) {
    a = a + v.at(i);
    val = (a + v.at(i + 1)) / 2;
  }
  cout << setprecision(6) << val << endl;
  return 0;
}
