a = int(input())
List=[int(i) for i in input().split()]
List.sort()
num = 0
ans = []
if a > 2:
 while num < a:
   res = (List[num] + List[num+1])/2
   ans.append(res)
   if num < a-2:
    resa = (ans[num] + List[num+2])/2
    num = num + 1
   else:
    break
 print(resa)
else:
 print((List[0] + List[1])/2)
