#include <bits/stdc++.h>
using namespace std;
int n;
int v[55];
double ans;
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> v[i];
  }
  sort(v, v + n);
  ans = (v[0] + v[1]) / 2.0;
  for (int i = 2; i < n; i += 2) {
    ans = (ans + v[i]) / 2.0;
  }
  printf("%.7f", ans);
  return 0;
}
