#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> a(n);
    rep(i,n) cin >> a[i];
    sort(a.begin(),a.end());
    set<int> st;
    rep(i,n) st.insert(a[i]);
    set<int> used;
    vector<int> ans;
    rep(i,n) {
        if(i==0) continue;
        if(used.count(a[i])) continue;
        for(int j=a[i];j<=m;j+=a[i]) {
            if(!st.count(j)) {
                cout << -1 << endl;
                return 0;
            }
            used.insert(j);
        }
        ans.push_back(a[i]);
    }
    cout << ans.size() << endl;
    for(int a : ans) {
        cout << a << " ";
    }
    cout << endl;
    return 0;
}