n = int(input())
i = list(map(int, input().split()))
n -= 1
i.sort()

for j in range(n):
    if(j<n-1):
        tmp = (i[j]+i[j+1])/2
        i.append(tmp)
        del i[0:2]
    i.sort()

ans = (i[0]+i[1])/2
print(ans)
