#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;
#define rep(i, s, t) for (ll i = s; i < (ll)(t); i++)

template<typename T>
bool chmin(T &x, T y) { return x > y ? (x = y, true) : false; }
template<typename T>
bool chmax(T &x, T y) { return x < y ? (x = y, true) : false; }

struct io_setup {
	io_setup() {
		ios::sync_with_stdio(false);
		std::cin.tie(nullptr);
		cout << fixed << setprecision(15);
	}
} io_setup;

using mint = atcoder::modint1000000007;

int main(){
	int n,m;
	cin>>n>>m;
	vector<int> a(n);
	rep(i,0,n) cin>>a.at(i);
	set<int> st;
	rep(i,1,n) st.insert(a.at(i));
	auto cst=st;
	vector<int> b;
	while(!st.empty()){
		int nw=*st.begin();
		for(int i=nw;i<=m;i+=nw){
			if(!cst.count(i)){
				cout<<"-1\n";
				return 0;
			}
			st.erase(i);
		}
		b.push_back(nw);
	}
	cout<<b.size()<<"\n";
	for(auto x:b) cout<<x<<" ";
	cout<<"\n";
}