#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  priority_queue<float> q;
  for (int i = 0; i < n; i++) {
    float y;
    cin >> y;
    q.push(y);
  }
  while (q.size() != 1) {
    float x = q.top();
    q.pop();
    float y = q.top();
    q.pop();
    float z = (float)(x + y) / 2;
    q.push(z);
  }
  cout << q.top() << endl;
  return 0;
}
