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

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

/* global variables */

int as[MAX_N], bs[MAX_N], xs[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);

  int k = 0;
  for (int i = 1; i < n; i++) {
    int c = 0;
    for (int j = 0; j < k; j++)
      if (as[i] % bs[j] == 0) {
	if (bs[j] * xs[j] != as[i]) { puts("-1"); return 0; }
	c++;
	xs[j]++;
      }

    if (c == 0)
      bs[k] = as[i], xs[k] = 2, k++;
  }

  for (int j = 0; j < k; j++)
    if (bs[j] * xs[j] <= m) { puts("-1"); return 0; }

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