#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
	int N,M;
	cin>>N>>M;
	vector<int> A(N);
	for(int i=0;i<N;i++) cin>>A[i];
	sort(A.begin(),A.end());
	vector<bool> P(N);
	unordered_map<int,int> m;
	for(int i=0;i<N;i++) m[A[i]] = i;
	vector<int> s = {};
	for(int i=1;i<N;i++)if(!P[i]){
		P[i] = true;
		s.push_back(A[i]);
		for(int j=A[i];j<=M;j+=A[i]){
			if(!m.count(j)){
				cout<<-1<<endl;
				return 0;
			}
			P[m[j]] = true;
		}
	}
	cout<<s.size()<<endl;
	for(int x:s) cout<<x<<' ';
	cout<<endl;
}