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

import itertools

p=itertools.permutations(v,len(v))
summary_l=[]

for q in p:
    summary=q[0]
    for i in range(1,N):
        summary=(summary+q[i])/2
    summary_l.append(summary)

print(max(summary_l))
