#include <bits/stdc++.h>
int main(void) {
  int N, a[51];
  scanf("%d", &N);
  int i, j, swap;
  for (i = 0; i < N - 1; i++) {
    scanf("%d ", &a[i]);
  }
  scanf("%d", &a[N - 1]);
  for (j = 0; j < N - 1; j++) {
    for (i = 0; i < N - 1 - j; i++) {
      if (a[i] > a[i + 1]) {
        swap = a[i];
        a[i] = a[i + 1];
        a[i + 1] = swap;
      }
    }
  }
  double temp;
  for (i = 0; i < N - 1; i++) {
    temp = ((double)a[i] + (double)a[i + 1]) / 2;
    a[i + 1] = temp;
  }
  printf("%lf\n", temp);
  return 0;
}
