N=int(input())
A=list(map(int,input().split()))
B=list(map(int,input().split()))
S=sum(A)-sum(B)

if N==2:
    if S==0:
        print(abs(A[0]-B[0]))
        exit()
    else:
        print(-1)
        exit()


if S%(N-2)!=0:
    print(-1)
    exit()
else:
    Q=S//(N-2)
    if Q<0:
        print(-1)
        exit()
    else:
        check=0
        for i in range(N):
            a=A[i]-Q
            b=B[i]
            if a>b or (b-a)%2==1:
                print(-1)
                exit()
            else:
                check+=(b-a)//2
        if check==Q:
            print(Q)
            exit()
        else:
            print(-1)
            exit()