import sys
input = sys.stdin.readline

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

USED=set()
ko=0
SET=set(A)
ANS=[]

for i in range(1,M+1):
    if M//i>N:
        continue

    flag=1

    for j in range(10**9+1):
        if i*j>M:
            break
        if i*j in SET:
            if i*j in USED:
                pass
            else:
                flag+=1
        else:
            flag=0
            break

    if flag>1:
        ANS.append(i)

        for j in range(10**9+1):
            if i*j>M:
                break
            USED.add(i*j)

    if len(USED)==len(SET):
        print(len(ANS))
        print(*ANS)
        exit()

print(-1)