#include <bits/stdc++.h>
int main(void) {
  int n;
  int v[1001];
  double ans;
  int tmp;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &v[i]);
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i; j <= n; j++) {
      if (v[i] > v[j]) {
        tmp = v[i];
        v[i] = v[j];
        v[j] = tmp;
      }
    }
  }
  ans = (((double)v[1]) + ((double)v[2])) / 2;
  for (int i = 2; i < n; i++) {
    ans = (ans + ((double)v[i + 1])) / 2;
  }
  printf("%fd\n", ans);
  return 0;
}
