#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  cin >> n;
  long long int v[n];
  long double a[n];
  long double sum = 0, ans = 0;
  for (long long int i = 0; i < n; i++) v[i] = i + 1;
  for (long long int i = 0; i < n; i++) cin >> a[i];
  do {
    sum = 0;
    for (long long int i = 0; i < n; i++) {
      if (i)
        sum = (sum + a[v[i] - 1]) / 2;
      else
        sum += a[v[i] - 1];
    }
    ans = max(sum, ans);
  } while (next_permutation(v, v + n));
  cout << setprecision(12) << ans;
}
