#include <bits/stdc++.h>
using namespace std;
int a[1010], n;
double b[1010];
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  sort(a + 1, a + n + 1);
  int p1 = 1, p2 = 2;
  while (p2 <= n) {
    b[p2] = ((double)a[p1] + (double)a[p2]) / 2;
    p1++, p2++;
  }
  printf("%lf \n", b[n]);
  return 0;
}
