#include <bits/stdc++.h>
using namespace std;
int i, j, nr, pp, n, m, nr1, v[100001], k = 1, poz = 1, h[100001], cate;
int main() {
  scanf("%d%d", &n, &m);
  for (i = 1; i <= n; i++) scanf("%d", &v[i]);
  sort(v + 1, v + n + 1);
  while (k <= m) {
    if (k == v[poz])
      poz++;
    else {
      cate++;
      h[cate] = k;
      m -= k;
    }
    k++;
  }
  printf("%d\n", cate);
  for (i = 1; i <= cate; i++) printf("%d ", h[i]);
  return 0;
}
