n, m = map(int, input().split())
A = list(map(int, input().split()))
A.sort()
se = set(A)
se2 = set()
B = []
for a in A[1:]:
    if a in se2:
        continue

    for b in range(a, m + 1, a):
        if b not in se:
            print(-1)
            exit()
        se2.add(b)

    B.append(a)

print(len(B))
print(*B)