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)
    dec = 0
    add = [0] * N
    for i in range(N):
        if A[i] < B[i]:
            dec += B[i] - A[i]
            add[i] += 2 * (B[i] - A[i])
    if dec > K:
        return -1
    return K
    # K -= dec
    # for i in range(N):
    #     A[i] += add[i] - dec
    # print(A, dec)
    # print(B)


print(main())