N, M = map(int, input().split())
A = list(map(int, input().split()))
A.sort()
if A[0] != 0:
    print(-1)
    exit()
AS = set(A)

B = set()
for a in A:
    if a == 0:
        continue
    f = False
    for b in B:
        if a % b == 0:
            f = True
            break
    if f:
        continue
    f = False
    for i in range(2, M // a + 1):
        if i * a not in AS:
            f = True
            break
    if f:
        print(-1)
        exit()
    else:
        B.add(a)
if len(B) == 0:
    print(-1)
else:
    print(len(B))
    print(*sorted(list(B)))