#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
istream &operator>>(istream &is, modint &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint &a) { return os << a.val(); }
istream &operator>>(istream &is, modint998244353 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint998244353 &a) { return os << a.val(); }
istream &operator>>(istream &is, modint1000000007 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint1000000007 &a) { return os << a.val(); } 

typedef long long ll;
typedef vector<vector<int>> Graph;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define FOR(i,l,r) for (int i = l;i < (int)(r); i++)
#define rep(i,n) for (int i = 0;i < (int)(n); i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define my_sort(x) sort(x.begin(), x.end())
#define my_max(x) *max_element(all(x))
#define my_min(x) *min_element(all(x))
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const int INF = (1<<30) - 1;
const ll LINF = (1LL<<62) - 1;
const int MOD = 998244353;
const int MOD2 = 1e9+7;
const double PI = acos(-1);
vector<int> di = {1,0,-1,0};
vector<int> dj = {0,1,0,-1};

#ifdef LOCAL
#  include <debug_print.hpp>
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

// A ^ N を M で割ったあまり
template<class T> T pow_mod(T A, T N, T M) {
    T res = 1 % M;
    A %= M;
    while (N) {
        if (N & 1) res = (res * A) % M;
        A = (A * A) % M;
        N >>= 1;
    }
    return res;
}

// Miller-Rabin 素数判定
bool Miller_Rabin(long long N) {
    if (N <= 1) return false;
    if (N == 2) return true;
    if (N % 2 == 0) return false;
    vector<long long> A = {2, 325, 9375, 28178, 450775,
                           9780504, 1795265022};
    long long s = 0, d = N - 1;
    while (d % 2 == 0) {
        ++s;
        d >>= 1;
    }
    for (auto a : A) {
        if (a % N == 0) return true;
        long long t, x = pow_mod<__int128_t>(a, d, N);
        if (x != 1) {
            for (t = 0; t < s; ++t) {
                if (x == N - 1) break;
                x = __int128_t(x) * x % N;
            }
            if (t == s) return false;
        }
    }
    return true;
}

int main(){
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    int N, M; cin >> N >> M;
    vector<int> A(N);
    rep(i, N) cin >> A[i];
    sort(all(A));

    vector<bool> check(N);
    vector<int> ans;
    FOR(i, 1, N)if(!check[i]){
        ans.push_back(A[i]);
        int cnt = 1;
        FOR(j, i + 1, N)if((A[j] % A[i]) == 0) {
            check[j] = true;
            cnt++;
        }
        if(M / A[i] != cnt) {
            cout << -1 << endl;
            return 0;
        }
    }

    int L = ans.size();
    cout << L << endl;
    rep(i, L) cout << ans[i] << (i == L - 1 ? "\n" : " ");
}