#include <bits/stdc++.h>
using namespace std;
int const maxn = 100;
int n;
double a[maxn], Max = -1;
void dfs(double st[]) {
  int i, j, cnt = 0;
  double b[maxn];
  for (i = 1; i <= n; i++) {
    b[i] = st[i];
    if (b[i] == 0) cnt++;
  }
  if (cnt == n - 1) {
    for (i = 1; i <= n; i++) {
      if (b[i]) {
        Max = max(Max, b[i]);
        return;
      }
    }
  }
  for (i = 1; i <= n; i++) {
    if (!st[i]) continue;
    for (j = 1; j <= n; j++) {
      if (!st[j] || i == j) continue;
      b[i] = (st[i] + st[j]) / 2;
      b[j] = 0;
      dfs(b);
      b[i] = st[i];
      b[j] = st[j];
    }
  }
  return;
}
int main() {
  cin >> n;
  int i;
  for (i = 1; i <= n; i++) cin >> a[i];
  dfs(a);
  cout << Max;
  return 0;
}
