#include <bits/stdc++.h>
using namespace std;
long long int n;
long long int a[55];
long long int vis[55];
double ans = 0.0;
void dfs(long long int k, double temp) {
  bool flag = false;
  for (long long int i = 1; i <= n; i++) {
    if (!vis[i]) {
      double res = (temp + a[i]) / 2;
      vis[i] = 1;
      flag = 1;
      dfs(i, res);
      vis[i] = 0;
    }
  }
  if (!flag) ans = max(ans, temp);
}
int32_t main() {
  cin >> n;
  for (long long int i = 1; i <= n; i++) cin >> a[i];
  for (long long int i = 1; i <= n; i++) {
    vis[i] = 1;
    dfs(i, a[i]);
    vis[i] = 0;
  }
  cout << fixed << setprecision(10) << ans;
}
