#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int 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());
	set<int> s;
	vector<int> ans;
	bool isok = true;
	for (int i = 0; i < n; i++) {
		if (a[i] == 0) continue;
		if (s.count(a[i])) continue;
		if (m / a[i] > n) {
			isok = false;
			break;
		}
		ans.push_back(a[i]);
		for (int j = 1; (ll)j * a[i] <= m; j++) {
			s.insert(j * a[i]);
		}
	}
	set<int> sa;
	for (int i = 0; i < n; i++) {
		sa.insert(a[i]);
	}
	for (auto v : s) {
		if (!sa.count(v)) {
			isok = false;
			break;
		}
	}
	if (isok) {
		int sz = ans.size();
		cout << sz << endl;
		for (int i = 0; i < sz; i++) {
			cout << ans[i];
			if (i == sz - 1)
				cout << endl;
			else
				cout << " ";
		}
	} else {
		cout << -1 << endl;
	}
	return 0;
}