#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;
using i8 = int8_t;
using i32 = int;
using i64 = long long;
// using i128 = __int128;
using u64 = unsigned long long;
using ll = long long;

void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  _main();
}

i64 pow(i64 j, i64 n) {
  i64 res = 1;
  while (n > 0) {
    if (n & 1)
      res *= j;
    j *= j;
    n >>= 1;
  }
  return res;
}

i64 n, m;
void _main() {
  cin >> n >> m;
  set<i64> a;
  bool zero = false;
  for (i64 i = 0; i < n; i++) {
    i64 b;
    cin >> b;
    if (b == 0) {
      zero = true;
      continue;
    }
    a.insert(b);
  }
  set<i64> b = a;
  if (zero) {
    b.insert(0);
  }
  vector<i64> ans;
  while (!a.empty()) {
    i64 x = *a.begin();
    ans.push_back(x);
    for (i64 i = 0; x * i <= m; i++) {
      if (!b.count(x * i)) {
        cout << "-1\n";
        return;
      }
      if (a.count(x * i)) {
        a.erase(x * i);
      }
    }
  }
  cout << ans.size() << "\n";
  for (i64 i = 0; i < ans.size(); i++) {
    cout << ans[i] << (i + 1 == ans.size() ? "\n" : " ");
  }
}