#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < (n); ++i) cin >> v[i];
  sort(v.begin(), v.end());
  double ans = 0;
  for (int i = 0; i < (n - 1); ++i) {
    if (i == 0)
      ans += (v[i] + v[i + 1]) / 2;
    else
      ans = (ans + v[i + 1]) / 2;
  }
  cout << ans << endl;
  return 0;
}
