N,M = map(int,input().split())
A = list(map(int,input().split()))
import sys
A = A[1:]
s = set(A)
A.sort()
d = set()

ans = []
for i in range(N - 1):
	a = A[i]
	if a not in d:
		ans.append(a)
		u = a
		while u <= M:
			if u not in s:
				print(-1)
				exit()
			else:
				d.add(u)
			u += a
print(len(ans))
print(*ans)