#include <bits/stdc++.h>
using namespace std;
void solve();
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve();
  return 0;
}
long double w[100];
int n;
long double m;
bool used[100];
void dfs(int l, int r, long double s) {
  for (int i = 1; i <= n; i++) {
    if (!used[i]) {
      s = (s + w[i]) / 2;
      used[i] = true;
      dfs(l, r, s);
    }
  }
  m = max(m, s);
}
void solve() {
  cin >> n;
  long double s = 0;
  for (int i = 1; i <= n; i++) cin >> w[i];
  for (int i = 1; i <= n; i++) {
    for (int j = i + 1; j <= n; j++) {
      for (int u = 1; u <= n; u++) used[u] = false;
      used[i] = true;
      used[j] = true;
      s = (w[i] + w[j]) / 2;
      dfs(i, j, s);
    }
  }
  cout << fixed << setprecision(5) << m;
}
