#include<iostream>
#include<set>
#include<vector>
#include<cassert>
using namespace std;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N,M;
	cin>>N>>M;
	set<int>EX;
	for(int i=0;i<N;i++)
	{
		int a;cin>>a;
		if(a)EX.insert(a);
	}
	set<int>rest=EX;
	vector<int>ans;
	while(!rest.empty())
	{
		int a=*rest.begin();
		ans.push_back(a);
		for(int b=a;b<=M;b+=a)
		{
			if(EX.find(b)==EX.end())
			{
				cout<<-1<<endl;
				return 0;
			}
			rest.erase(b);
		}
	}
	cout<<ans.size()<<"\n";
	for(int i=0;i<ans.size();i++)cout<<ans[i]<<(i+1==ans.size()?"\n":" ");
}