#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
#include <cmath>
using namespace std;

const long long inf = 1e18;
const int mod = 998244353;

int N, M;
vector<int> A;
set<int> AS, ok, ng;

int judge(int a) {
    vector<int> num;
    for (int i = 2; i * i <= a; ++i) {
        if (a % i != 0) continue;
        if (ng.find(i) == ng.end()) num.push_back(i);
        if (a / i != i && ng.find(a / i) == ng.end()) num.push_back(a / i);
    }
    num.push_back(a);
    sort(num.begin(), num.end());
    for (int j : num) {
        int tmp = j;
        while (tmp <= A.back()) {
            if (AS.find(tmp) == AS.end()) {
                ng.insert(j);
                break;
            }
            tmp += j;
        }
        if (ng.find(j) != ng.end()) continue;
        tmp = j;
        while (tmp <= A.back()) {
            ok.insert(tmp);
            tmp += j;
        }
        return j;
    }
    return -1;
}

int main() {
    cin >> N >> M;
    A.resize(N);
    for (int i = 0; i < N; ++i) cin >> A[i];
    sort(A.begin(), A.end());
    AS = set<int>(A.begin(), A.end());
    
    vector<int> ans;
    for (int i = 1; i < N; ++i) {
        if (ok.find(A[i]) != ok.end()) continue;
        int res = judge(A[i]);
        if (res == -1) {
            cout << -1 << endl;
            return 0;
        }
        ans.push_back(res);
    }
    sort(ans.begin(), ans.end());
    cout << ans.size() << endl;
    for (int a : ans) cout << a << " ";
    cout << endl;
    return 0;
}