import heapq

N = int(input())
v = list(map(int, input().split()))

heapq.heapify(v)

res = 0
for _ in range(int(N/2)+1):
  a = heapq.heappop(v)
  b = heapq.heappop(v)
  res = (a+b)/2
  heapq.heappush(v, res)
    
print(res)