#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <set>
#include <map>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)

void solve(){
    
}

int main(){
    int n, m; cin >> n >> m;
    vi v(n-1);
    rep(i, n){
        int a; cin >> a;
        if(i >= 1)v[i-1] = a;
    }sort(all(v));
    map<int, int> mp; rep(i, n-1)mp[v[i]] = i;
    vi ans;
    vector<bool> vb(n-1, false);
    int itr = 0;
    while(itr < n-1){
        int u = v[itr];
        if(vb[itr]){
            itr++;
            continue;
        }
        vb[itr] = true;
        if(m/u > n){
            cout << -1 << endl;
            return 0;
        } 
        ans.push_back(u);
        for(int i = 2*u; i <=m; i+= u){
            if(!mp.count(i)){
                cout << -1 << endl;
                return 0;
            }
            vb[mp[i]] = true;
        }
        itr++;
    }
    cout << ans.size() << endl;
    for(auto i : ans)cout << i << " ";
    cout << endl;

    return 0;
}