#include <bits/stdc++.h>
int compare_int(const void *a, const void *b) { return *(int *)a - *(int *)b; }
int main() {
  int N, i;
  float v[1000];
  float price = 0;
  scanf("%d", &N);
  for (i = 0; i < N; i++) {
    scanf("%f", &v[i]);
  }
  qsort(v, N, sizeof(int), compare_int);
  for (i = 1; i < N - 1; i++) {
    if (v[i] - v[i - 1] > v[i + 1] - v[i]) {
      v[i + 1] = (v[i + 1] + v[i]) / 2;
      v[i] = v[i - 1];
    } else {
      v[i] = (v[i - 1] + v[i]) / 2;
      v[i - 1] = -1000000;
    }
  }
  printf("%f \n", (v[N - 1] + v[N - 2]) / 2);
  return 0;
}
