n=int(input())
aaa = input()
a = [int(n) for n in aaa.split()]
bbb = input()
b = [int(n) for n in bbb.split()]
k=n
aa=0
while k :
    k-=1
    aa+=a[k]
k=n
bb=0
while k :
    k-=1
    bb+=b[k]
ans=(3*aa-2*bb)/(aa-bb)
print("%.6f"%ans)

没法单独读取啊