def main():
    N = int(input())
    D = list(map(int, input().split()))
    x, y = map(int, input().split())
    if (x, y) == (0, 0):
        return 0

    P = abs(x + y)
    Q = abs(x - y)
    if P > Q:
        P, Q = Q, P

    if Q in D:
        return 1

    dmax = max(D)
    if Q <= dmax:
        return 2

    return -1


print(main())