n = int(input())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

S = 0
for a, b in zip(A, B):
    S += a-b
#print(S)
if S%(n-2) == 0:
    x = S//(n-2)
    for a, b in zip(A, B):
        if b-a+x < 0:
            print(-1)
            exit()
        else:
            if (b-a+x)%2 != 0:
                print(-1)
                exit()
    else:
        print(x)
else:
    print(-1)