#include <bits/stdc++.h>
using namespace std;

void fast_io() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
}

int main() {
	fast_io();
	int n, m;
	cin >> n >> m;
	set<int> not_vis, vis;
	for (int i = 0; i < n; i++) {
		int a;
		cin >> a;
		if (i) {
			not_vis.insert(a);
		}
	}
	vector<int> ans;
	while (!not_vis.empty()) {
		int d = *not_vis.begin();
		ans.push_back(d);
		int num = d;
		while (num <= m) {
			if (not_vis.count(num) == 0 && vis.count(num) == 0) {
				cout << -1 << endl;
				return 0;
			}
			if (not_vis.count(num)) {
				not_vis.erase(num);
				vis.insert(num);
			}
			num += d;
		}
	}
	cout << ans.size() << endl;
	for (int i : ans) {
		cout << i << " ";
	}
	cout << endl;
}