#include <iostream>
#include <vector>
#include <set>
#include <algorithm>

using namespace std;

int main()
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int N, M, i, cur;
    cin >> N >> M;
    set<int> rest;
    vector<int> A(N), B;
    for (i = 0; i != N; ++i)
        cin >> A[i];

    sort(A.begin(), A.end());
    for (i = 1; i != N; ++i)
        rest.insert(A[i]);

    while (!rest.empty())
    {
        cur = *rest.begin(), rest.erase(rest.begin());
        for (i = 2; cur * i <= M; ++i)
        {
            if (!binary_search(A.begin(), A.end(), cur * i))
            {
                cout << "-1\n";
                return 0;
            }

            set<int>::iterator temp;
            if ((temp = rest.find(cur * i)) != rest.end())
                rest.erase(temp);
        }
        B.push_back(cur);
    }

    cout << B.size() << '\n' << B[0];
    for (i = 1; i != B.size(); ++i) cout << ' ' << B[i];
    cout << '\n';
    return 0;
}