/* -*- coding: utf-8 -*-
 *
 * 2806.cc:  No.2806 Cornflake Man - yukicoder
 */

#include<cstdio>
#include<unordered_map>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

using ll = long long;
using umii = unordered_map<int,int>;

/* global variables */

int as[MAX_N], bs[MAX_N];
bool used[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) scanf("%d", as + i);

  sort(as + 1, as + n);
  umii aps;
  for (int i = 1; i < n; i++) aps[as[i]] = i;

  int k = 0;
  for (int i = 1; i < n; i++) {
    if (! used[i]) {
      used[i] = true;
      for (int ax = as[i] * 2; ax <= m; ax += as[i]) {
	if (! aps.count(ax)) { puts("-1"); return 0; }
	used[aps[ax]] = true;
      }
      bs[k++] = as[i];
    }
  }

  printf("%d\n", k);
  for (int j = 0; j < k; j++)
    printf("%d%c", bs[j], (j + 1 < k) ? ' ' : '\n');
  
  return 0;
}