#include "bits/stdc++.h"
#define ff first
#define ss second
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()
using namespace std;
using ll = long long;
using pii = pair<int, int>;
const char nl = '\n';
const ll LINF = 0x3f3f3f3f3f3f3f3f;
const int INF = 0x3f3f3f3f;
int main() {
ios::sync_with_stdio(0), cin.tie(0);
int n; cin >> n;
vector<int> v(n); for (auto &x : v) cin >> x;
sort(all(v));
double ans = 0;
do {
double m;
for (int i = 0; i < n - 1; i++) {
if (i == 0) m = (double) (v[i] + v[i + 1]) / 2;
else m = (double) (m + v[i + 1]) / 2;
}
ans = max(ans, m);
} while (next_permutation(all(v)));
cout << fixed << setprecision(6) << ans << nl;
return 0;
}
