N,M = map(int,input().split())
B = list(map(int,input().split()))
B.sort()

check = [True for i in range(N)]
done = [True for i in range(N)]

state = True
out = []
for i in range(1,N):
    if done[i]:
        out.append(B[i])
        t = 2
        for j in range(i+1,N):
            if B[j] == t*B[i]:
                t += 1
                done[j] = False
            elif B[j] > t*B[i]:
                state = False
        if (t+1)*B[i] <= M:
            state = False


if state:
    print(len(out))
    [print(i, end=" ") for i in out]
else:print(-1)