#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18 + 5;
const long long mod = 1e9 + 7;
const long long N = 2e5 + 314;
const long double pi = 3.1415926535897932384626433832795;
void solve() {
  long long n;
  cin >> n;
  vector<long long> v(n);
  for (long long i = 0; i < n; i++) cin >> v[i];
  sort((v).begin(), (v).end());
  cout << fixed << setprecision(10);
  if (n > 2)
    cout << ((long double)(v[n - 2] + v[n - 3]) / 2 + v[n - 1]) / 2;
  else
    cout << ((long double)(v[n - 2] + v[n - 1])) / 2;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long t = 1;
  while (t--) solve();
}
