#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long n, m;
  cin >> n >> m;
  set<long long> have;
  while (n--) {
    long long kek;
    cin >> kek;
    have.insert(kek);
  }
  vector<long long> ans;
  long long need = 0, cur = 1;
  while (need <= m) {
    long long cost = have.count(cur) ? 0 : cur;
    need += cost;
    if (need > m) break;
    if (!have.count(cur)) ans.push_back(cur);
    cur++;
  }
  cout << ans.size() << '\n';
  for (auto e : ans) cout << e << " ";
  return 0;
}
