#include <bits/stdc++.h>
//#include <atcoder/all>
using ll = long long;
#define MOD 1000000007
#define Mod 998244353
const int MAX = 1000000005;
const long long INF = 1000000000000000005LL;
using namespace std;
//using namespace atcoder;
#define MOD 1000000007



int main() {
    ios::sync_with_stdio(0); cin.tie();
    int N, M;
    cin >> N >> M;
    vector<int> A(N);
    for (int i = 0; i < N; i++) cin >> A[i];
    set<int> se;
    for (int i = 0; i < N; i++) se.insert(A[i]);
    sort(A.begin(), A.end());
    map<int, int> mp;
    vector<int> ans;
    for (int i = 1; i < N; i++) {
        if (mp.count(A[i])) continue;
        mp[A[i]] = 1;
        ans.push_back(A[i]);
        for (int j = 2*A[i]; j <= M; j += A[i]) {
            if (!se.count(j)) {
                cout << -1 << endl;
                return 0;
            }
            if (mp.count(j)) continue;
            mp[j] = 1;
        }
    }
    sort(ans.begin(), ans.end());
    cout << ans.size() << endl;
    for (int i = 0; i < (int)ans.size(); i++) {
        cout << ans[i] << (i+1 == (int)ans.size() ? "\n" : " ");
    }
}