#include <bits/stdc++.h>
int main() {
  int min, s, t, u = 0;
  int N;
  scanf("%d", &N);
  double a[N];
  for (int i = 0; i < N; i++) {
    scanf("%lf", &a[i]);
  }
  while (N > 2) {
    for (int i = u; i < u + 2; i++) {
      min = a[i];
      s = i;
      for (int j = i + 1; j < N; j++) {
        if (a[j] < min) {
          min = a[j];
          s = j;
        }
      }
      t = a[i];
      a[i] = a[s];
      a[s] = t;
    }
    a[u + 1] = (a[u] + a[u + 1]) / 2;
    u++;
    N--;
  }
  printf("%lf", (a[u] + a[u + 1]) / 2);
  return 0;
}
