from heapq import heapify, heappush, heappop
n = int(input())
L = [int(i) for i in input().split()]
heapify(L)
for i in range(n-1):
    s = (L[0]+L[1])/2
    L = L[2:] 
    heappush(L,s)
ans = heapq.heappop(L)
print(ans)