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