a = int(input())
n = list(map(int, input().split()))
b=sorted(n,reverse=True)
ans=0
for i,j in enumerate (b):
    print(i,j)
    if i < a-1:
        ans += j*((1/2)**(i+1))
    if i ==a-1:
        ans += j*((1/2)**(i))
print(ans)