#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m; cin >> n >> m;
  vector<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  vector<int> ans;
  set<int> st(a.begin() + 1, a.end()), played;
  for (auto e : st) {
    if (played.count(e)) continue;
    ans.push_back(e);
    for (int i = 1; e * i <= m; i++) {
      if (not st.count(e * i)) {
        cout << -1 << endl;
        return 0;
      }
      played.insert(e * i);
    }
  }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i] << (i + 1 == ans.size() ? "\n" : " ");
  }
}