import heapq
n = raw_input()
heap = [x*(-1) for x in map(float, raw_input().split(' '))]
heapq.heapify(heap)
while(len(heap)>1):
	u,v = heapq.heappop(heap), heapq.heappop(heap)
	u*=-1
	v*=-1
	w = 0.5*(u+v)
	heapq.heappush(heap, -w)


print -heap[0]