#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main() {
	int n,m;
	cin >> n >> m;
	set<int> s;
	vector<int> a(n);
	for(int i = 0; i < n; i++) cin >> a[i], s.insert(a[i]);
	sort(a.begin(),a.end());
	set<int> v;
	int ans = 0;
	vector<int> an;
	for(int i = 1; i < n; i++) {
		if(v.count(a[i])) continue;
		for(int j = a[i]; j <= m; j+=a[i]) {
			if(!s.count(j)) {
				cout << -1 << endl;
				return 0;
			}
			v.insert(j);
		}
		ans++;
		an.push_back(a[i]);
	}
	cout << ans << endl;
	for(int i = 0; i < ans; i++) cout << an[i] << ' ';
	cout << endl;
}