#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n);
  vector<int> p(n);
  for (int i = 0; i < n; ++i) cin >> v[i];
  for (int i = 0; i < n; ++i) p[i] = i;
  double maxV = 0;
  while (1) {
    double value = v[p[0]];
    for (int i = 1; i < n; ++i) {
      int index = p[i];
      value += v[index];
      value /= 2.0;
    }
    maxV = max(value, maxV);
    if (!next_permutation(p.begin(), p.end())) break;
  }
  printf("%.10f\n", maxV);
  return 0;
}
