#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  int v[1100];
  double x;
  cin >> N;
  for (int i = 0; i < N; ++i) cin >> v[i];
  sort(v, v + N);
  for (int i = 0; i < N; i = i + 2) {
    x = x / 2 + v[i] / 2 + v[i + 1] / 2;
  }
  cout << x << endl;
}
