#include <bits/stdc++.h>
using namespace std;
int main() {
  set<long long> already_has, buy_new;
  long long n, m;
  cin >> n >> m;
  for (long long i = 0; i < n; i++) {
    long long x;
    cin >> x;
    already_has.insert(x);
  }
  for (long long i = 1; i <= 1000000000; i++) {
    if (m < i) break;
    if (already_has.count(i) == 0) {
      buy_new.insert(i);
      m -= i;
    }
  }
  cout << buy_new.size() << endl;
  for (long long i : buy_new) cout << i << " ";
  return 0;
}
