#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
#define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i)
#define rep(i, n) drep(i, 0, n - 1)
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
const ll MOD1000000007 = 1000000007;
const ll MOD998244353 = 998244353;
const ll MOD[3] = {999727999, 1070777777, 1000000007};
const ll LINF = 1LL << 60LL;
const int IINF = (1 << 30) - 1;


template<typename T> 
struct edge{
    int from;
    int to;
    T cost;
    int id;

    edge(){}
    edge(int to, T cost=1) : from(-1), to(to), cost(cost){}
    edge(int to, T cost, int id) : from(-1), to(to), cost(cost), id(id){}
    edge(int from, int to, T cost, int id) : from(from), to(to), cost(cost), id(id){}

    void reverse(){swap(from, to);}
};

template<typename T>
struct edges : std::vector<edge<T>>{
    void sort(){
        std::sort(
            (*this).begin(),
            (*this).end(), 
            [](const edge<T>& a, const edge<T>& b){
                return a.cost < b.cost;
            }
        );
    }
};

template<typename T>
struct graph : std::vector<edges<T>>{
    int n = 0;
    int m = 0;
    edges<T> es;
    bool directed;

    graph(int n, bool directed) : n(n), directed(directed){
        (*this).resize(n);
    }

    void add_edge(int from, int to, T cost=1){
        if(directed){
            es.push_back(edge<T>(from, to, cost, m));
            (*this)[from].push_back(edge<T>(from, to, cost, m++));
        }else{
            if(from > to) swap(from, to);
            es.push_back(edge<T>(from, to, cost, m));
            (*this)[from].push_back(edge<T>(from, to, cost, m));
            (*this)[to].push_back(edge<T>(to, from, cost, m++));
        }
    }
};

template<typename T>
struct redge{
    int from, to;
    T cap, cost;
    int rev;
    
    redge(int to, T cap, T cost=(T)(1)) : from(-1), to(to), cap(cap), cost(cost){}
    redge(int to, T cap, T cost, int rev) : from(-1), to(to), cap(cap), cost(cost), rev(rev){}
};

template<typename T> using Edges = vector<edge<T>>;
template<typename T> using weighted_graph = vector<Edges<T>>;
template<typename T> using tree = vector<Edges<T>>;
using unweighted_graph = vector<vector<int>>;
template<typename T> using residual_graph = vector<vector<redge<T>>>;


vector<long long> dijkstra(weighted_graph<long long> G, int src){
    int n = (int)G.size();

    vector<long long> dist(n, LINF);
    dist[src] = 0;
    priority_queue<pair<long long, int>, vector<pair<long long, int>>, greater<pair<long long, int>>> PQ;
    PQ.push({0, src});
    while(!PQ.empty()){
        int v = PQ.top().second;
        long long tmp = PQ.top().first;
        PQ.pop();
        if(dist[v] < tmp) continue;

        for(edge<long long> e : G[v]){
            if(dist[v]+e.cost < dist[e.to]){
                dist[e.to] = dist[v]+e.cost;
                PQ.push({dist[e.to], e.to});
            }
        }
    }

    return dist;
}


void solve(){
    int n, m; cin >> n >> m;
    vector<int> a(n);
    for(int i=0; i<n; i++) cin >> a[i];
    sort(all(a));

    map<int, bool> mp;
    for(int i=1; i<n; i++) mp[a[i]] = false;

    vector<int> ans;
    for(int i=1; i<n; i++) if(!mp[a[i]]){
        if(m/a[i]>n){
            cout << -1 << '\n';
            return;
        }

        for(int y=a[i]; y<=m; y+=a[i]){
            if(mp.find(y) != mp.end()){
                mp[y] = true;
            }else{
                cout << -1 << '\n';
                return;
            }
        }

        ans.pb(a[i]);
    }

    cout << (int)ans.size() << '\n';
    for(int v : ans) cout << v << ' ';
    cout << '\n';
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int T=1;
    //cin >> T;
    while(T--) solve();
}