#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

int main() {
    ll N, M;
    cin >> N >> M;
    vector<ll> A(N);
    for (int i = 0; i < N; i++) {
        cin >> A[i];
    }

    if (N > M + 1) {
        cout << -1 << endl;
        return 0;
    } else if (N == M + 1) {
        cout << 1 << endl
             << 1 << endl;
        return 0;
    }

    sort(A.begin(), A.end());
    set<ll> ext(A.begin(), A.end());
    set<ll> ans, seen;

    for (int i = 1; i < N; i++) {
        if (M / A[i] + 1 > N) {
            cout << -1 << endl;
            return 0;
        }
        if (!seen.count(A[i])) {
            ans.insert(A[i]);
            for (ll x = A[i]; x <= M; x += A[i]) {
                if (!ext.count(x)) {
                    cout << -1 << endl;
                    return 0;
                }
                seen.insert(x);
            }
        }
    }

    cout << ans.size() << endl;
    for (int x : ans) {
        cout << x << ' ';
    }
    cout << endl;
}