#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = (int)1e9 + 1001010;
const ll llINF = (long long)4e18 + 22000020;
const string endn = "\n";
template <class T> inline auto vector2(size_t i, size_t j, const T &init = T()) {return vector(i, vector<T>(j, init));}
const string ELM_SEP = " ", VEC_SEP = endn;
template<class T> istream& operator >>(istream &i, vector<T> &A) {for(auto &I : A) {i >> I;} return i;}
template<class T> ostream& operator <<(ostream &o, const vector<T> &A) {int i=A.size(); for(const auto &I : A){o << I << (--i ? ELM_SEP : "");} return o;}
template<class T> ostream& operator <<(ostream &o, const vector<vector<T>> &A) {int i=A.size(); for(const auto &I : A){o << I << (--i ? VEC_SEP : "");} return o;}
template<class T> vector<T>& operator ++(vector<T> &A, int n) {for(auto &I : A) {I++;} return A;}
template<class T> vector<T>& operator --(vector<T> &A, int n) {for(auto &I : A) {I--;} return A;}
template<class T, class U> bool chmax(T &a, const U &b) {return ((a < b) ? (a = b, true) : false);}
template<class T, class U> bool chmin(T &a, const U &b) {return ((a > b) ? (a = b, true) : false);}
ll floor(ll a, ll b){if (b < 0) a = -a, b = -b; if(a >= 0) return a / b; else return (a + 1) / b - 1;}
ll ceil(ll a, ll b){if (b < 0) a = -a, b = -b; if(a > 0) return (a - 1) / b + 1; else return a / b;}
ll bit(unsigned long long val, unsigned long long digit){return (val >> digit) & 1;}
#ifdef DEBUG
#include <cpp-dump/dump.hpp>
#define dump(...) cpp_dump(__VA_ARGS__)
namespace cp = cpp_dump;
struct InitCppDump{
    InitCppDump(){
        if(!isatty(fileno(stderr))) CPP_DUMP_SET_OPTION(es_style, cpp_dump::es_style_t::no_es);
        CPP_DUMP_SET_OPTION(log_label_func, cp::log_label::line());
        CPP_DUMP_SET_OPTION(max_iteration_count, 30);
    }
} init_cpp_dump;
#else
#define dump(...)
#endif
// ================================== ここまでテンプレ ==================================


int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll n, m; cin >> n >> m;
    set<ll> a;
    for(int i = 0; i < n; i++){
        int tmp; cin >> tmp;
        a.emplace(tmp);
    }

    vector<ll> b;
    set<ll> used;
    for(auto val : a){
        if(val == 0) continue;
        if(used.count(val)) continue;

        b.emplace_back(val);
        for(ll i = 2*val; i <= m; i+=val){
            if(!a.count(i)){
                cout << -1 << endl;
                return 0;
            }
            else{
                used.emplace(i);
            }
        }
    }

    cout << b.size() << endl;
    cout << b << endl;
    return 0;
}