def main():
    N = int(input())

    if N == 1:
        a = int(input())
        b = int(input())
        if b < a:
            return -1
        return b - a

    A = list(map(int, input().split()))
    B = list(map(int, input().split()))
    sa = sum(A)
    sb = sum(B)
    if N == 2:
        if sa != sb:
            return -1
        return abs(A[0] - B[0])

    if sb > sa:
        return -1
    if (sa - sb) % (N - 2) != 0:
        return -1

    K = (sa - sb) // (N - 2)
    A = [a - K for a in A]

    tmp = 0
    for a, b in zip(A, B):
        op = b - a
        if op < 0:
            return - 1
        tmp += op // 2
    if K == tmp:
        return K
    return -1


print(main())