#include <bits/stdc++.h>
using namespace std;
priority_queue<double> q;
int n;
int main() {
  scanf("%d", &n);
  for (register int i = 1, x; i <= n; i++) {
    scanf("%d", &x);
    q.push(-x);
  }
  while (q.size() > 1) {
    int x = -q.top();
    q.pop();
    int y = -q.top();
    q.pop();
    q.push(-(x + y) * 0.5);
  }
  printf("%.6lf", -q.top());
  return 0;
}
