import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#sys.setrecursionlimit(10**9)
#sys.set_int_max_str_digits(0)
#input = sys.stdin.readline
#n = int(input())
#
#alist = []
input = sys.stdin.readline

n,m = map(int,input().split())
a = list(map(int,input().split()))
a.sort()
b = []
check = [0 for i in range(n)]
check[0] = 1
c = collections.defaultdict(lambda :-1)
for i in range(n):
    c[a[i]] = i
for i in range(1,n):
    if check[i] == 0:
        x = a[i]
        while x <= m:
            check[c[x]] = 1
            if c[x] == -1:
                exit(print(-1))
            x += a[i]
        b.append(a[i])
print(len(b))
print(*b)