#include <bits/stdc++.h>
int main() {
  int n, i, k, j;
  double a[1005];
  double t, s;
  scanf("%d", &n);
  for (i = 0; i < n; i++) scanf("%lf", &a[i]);
  for (i = 0; i < n - 1; i++) {
    for (j = n - 1; j > i; j--) {
      if (a[j] < a[j - 1]) {
        t = a[j];
        a[j] = a[j - 1];
        a[j - 1] = t;
      }
    }
  }
  for (i = 0; i < n - 1; i++) {
    s = (double)(a[i] + a[i + 1]) / 2;
    if (i + 1 == n - 1) break;
    a[i] = 0;
    k = i + 1;
    while (k < n && a[k + 1] < t) k++;
    for (j = k - 1; j > i; j--) {
      t = a[j];
      a[j] = a[j - 1];
      a[j - 1] = t;
    }
    a[k] = s;
  }
  printf("%f\n", s);
  return 0;
}
