#include <bits/stdc++.h>
using namespace std;
int main() {
  int a;
  cin >> a;
  vector<double> N(a);
  for (int i = 0; i < a; i++) {
    cin >> N.at(i);
  }
  sort(N.begin(), N.end());
  double ans1 = 0;
  for (int i = 0; i < a; i++) {
    ans1 += N.at(i);
  }
  double ans2 = 0;
  for (int i = 0; i < a - 1; i++) {
    ans2 += N.at(i);
  }
  if (a % 2 == 0) {
    cout << ans1 / 4 << endl;
  } else {
    cout << (ans2 + 2 * N.at(a - 1)) / 4 << endl;
  }
}
