#include <bits/stdc++.h>
using namespace std;

// 想定解
int main() {
    int N, M;
    cin >> N >> M;
    vector<int> A(N);
    for(int i = 0; i < N; i++)
        cin >> A[i];
    sort(A.begin(), A.end());
    vector<int> B;
    vector<bool> verified(N);
    for(int i = 1; i < N; i++) {
        if(verified[i])
            continue;
        for(int j = A[i]; j <= M; j += A[i]) {
            if(!binary_search(A.begin(), A.end(), j)) {
                cout << -1 << endl;
                return 0;
            }
            verified[lower_bound(A.begin(), A.end(), j) - A.begin()] = true;
        }
        B.emplace_back(A[i]);
    }
    cout << B.size() << endl;
    for(int i = 0; i < (int)B.size(); i++) {
        cout << B[i];
        if(i != (int)B.size() - 1)
            cout << ' ';
    }
    cout << endl;
}