#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  double a[n + 1];
  for (int i = 0; i < n; i++) cin >> a[i];
  a[n] = 1234;
  sort(a, a + n);
  a[n] = 0;
  while (n > 1) {
    n = (n + 1) / 2;
    for (int i = 0; i < n; i++) {
      if (a[2 * i + 1] != 0)
        a[i] = 0.5 * (a[2 * i] + a[2 * i + 1]);
      else
        a[i] = a[2 * i];
    }
  }
  cout << std::fixed << std::setprecision(10) << a[0] << endl;
}
