N,M = map(int,input().split())
A = sorted(list(map(int,input().split())))
C = {}
for i in range(1,N):
    C[A[i]] = 0
B = []
flag = 1
for i in range(1,N):
    if C[A[i]]==0:
        C[A[i]] = 1
        B.append(A[i])
        for j in range(2*A[i],M+1,A[i]):
            if j not in C:
                flag = -1
                break
            C[j] = 1
    if flag==-1:break
if flag==-1:
    print(flag)
else:
    print(len(B))
    print(*B)