#include<bits/stdc++.h>
using namespace std;
int main(){
	int n, m;
	cin >> n >> m;
	assert(2 <= n && n <= 200000);
	assert(1 <= m && m <= 1000000000);
	vector<int> a(n);
	for(int i = 0; i < n; i++){
		cin >> a[i];
		assert(0 <= a[i] && a[i] <= m);
	}
	assert(a[0] == 0);
	sort(a.begin(), a.end());
	map<int, int> m2;
	for(int i = 0; i < n; i++){
		m2[a[i]] = i;
	}
	vector<int> seen(n);
	seen[0] = 1;
	vector<int> ans;
	for(int i = 0; i < n; i++){
		if(seen[i]) continue;
		ans.push_back(a[i]);
		int x = 2*a[i];
		for(int j = x; j <= m; j += a[i]){
			if(!m2.count(j)){
				cout << -1 << '\n';
				return 0;
			}
			seen[m2[j]] = 1;
		}
	}
	cout << (int)ans.size() << '\n';
	for(auto x:ans) cout << x << " ";
	cout << '\n';
}