import itertools
N=int(input())
gu=list(map(int,input().split()))
ans=[]
for v in itertools.permutations(gu):
    cnt=2
    k=(v[0]+v[1])/2
    while cnt<=N-1:
        k=(k+v[cnt])/2
        cnt+=1
    ans.append(k)
print(max(ans))        
        