## https://yukicoder.me/problems/no/2806

MOD = 998244353      


def main():
    N, M = map(int, input().split())
    A = list(map(int, input().split()))

    A.sort()
    a_map = {}
    for i in range(N):
        a_map[A[i]] = i

    used = [False] * N
    used[0] = True
    answer = []
    for i in range(N):
        if used[i]:
            continue
        
        x = A[i]
        answer.append(A[i])
        while x <= M:
            if x in a_map:
                index = a_map[x]
                used[index] = True
            else:
                print(-1)
                return
            x += A[i]
    print(len(answer))
    print(" ".join(map(str, answer)))


        




        

        

        







if __name__ == "__main__":
    main()