#include <bits/stdc++.h>
using namespace std;
long double p[20], kq, a[100000];
int cd;
int main() {
  cin >> cd;
  for (int i = 1; i <= cd; i++) {
    cin >> a[i];
  }
  p[0] = 1;
  for (int i = 1; i <= cd; i++) {
    p[i] = p[i - 1] * 2;
  }
  sort(a + 1, a + 1 + cd);
  int t = 1;
  for (int i = cd; i >= 3; i--) {
    kq += a[i] / p[t];
    t++;
  }
  kq += a[1] / p[t] + a[2] / p[t];
  cout << fixed << setprecision(9);
  cout << kq;
}
