#include <bits/stdc++.h>
using namespace std;
int book[1005], n, a[1005];
float sum = 0, t;
bool f = true;
unsigned long long b[1005];
void dfs(int step) {
  int i;
  if (step == n + 1) {
    sum = (a[1] + a[2]) / 2.0;
    for (i = 3; i <= n; i++) {
      sum = (sum + a[i]) / 2.0;
    }
    if (f) {
      t = sum;
      f = false;
    } else {
      if (sum > t) t = sum;
    }
    return;
  }
  for (i = 1; i <= n; i++) {
    if (book[i] == 0) {
      a[step] = b[i];
      book[i] = 1;
      dfs(step + 1);
      book[i] = 0;
    }
  }
  return;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    cin >> b[i];
  }
  dfs(1);
  cout << t;
  return 0;
}
