#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, x, c = 0, c1 = 0;
  cin >> n >> m;
  pair<set<int>::iterator, bool> pr;
  set<int> s;
  set<int>::iterator s_it;
  for (int j = 1; j <= n; j++) {
    cin >> x;
    s.insert(x);
  }
  int i = 1;
  while (m - i >= 0) {
    pr = s.insert(i);
    if (pr.second == true) {
      c++;
      m = m - i;
    } else
      s.erase(i);
    i++;
  }
  cout << c << endl;
  if (c == 0) return 0;
  for (s_it = s.begin(); s_it != s.end(); s_it++) {
    cout << *s_it << ' ';
    c1++;
    if (c1 == c) return 0;
  }
  return 0;
}
