n=int(input())
a,b=[list(map(int,input().split())) for i in range(2)]
if n==2:
    if sum(a)==sum(b):
        print(sum(A-B for A,B in zip(a,b)if A>B))
    else:print(-1)
else:
    v=sum(a)-sum(b)
    if v<0 or v%(n-2):print(-1)
    else:
        k=v//(n-2)
        f=k
        for x,y in zip(a,b):
            if (x-y-k)%2 or k+min(x-y,y-x)<0:print(-1);exit()
            bc=(y-x+k)//2
            if f<bc:print(-1);exit()
            f-=bc
        print(-1 if f else k)