#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll n, m;
  cin >> n >> m;
  set<ll> st, used;
  rep(i, n) {
    ll a;
    cin >> a;
    st.insert(a);
  }
  used.insert(0);
  vector<ll> ans;
  for (const auto a : st)
    if (used.count(a) == 0) {
      ans.push_back(a);
      for (ll x = a; x <= m; x += a) {
        if (st.count(x) == 0) {
          cout << -1 << '\n';
          return;
        }
        used.insert(x);
      }
    }
  cout << ans.size() << '\n';
  rep(i, ans.size()) cout << (i ? " " : "") << ans[i];
  cout << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}