#include <bits/stdc++.h>
using namespace std;
int n, m, i, a[100001];
int h, pc, q, juc[100001];
int main() {
  cin >> n >> m;
  for (i = 1; i <= n; i++) {
    cin >> a[i];
  }
  sort(a + 1, a + n + 1);
  h = 1;
  while (pc < m) {
    pc++;
    if (pc == a[h])
      h++;
    else {
      m -= pc;
      juc[++q] = pc;
    }
  }
  cout << q << '\n';
  for (i = 1; i <= q; i++) cout << juc[i] << " ";
  return 0;
}
