#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  long long cnt, x;
  map<long long, int> a;
  vector<long long> res;
  cin >> n >> m;
  for (int i = 0; i < n; ++i) {
    cin >> x;
    a[x] = 1;
  }
  cnt = 1;
  while (m - cnt >= 0) {
    if (!(a.count(cnt))) {
      m -= cnt;
      res.push_back(cnt);
    }
    cnt++;
  }
  cout << res.size() << endl;
  for (int i = 0; i < res.size(); ++i) {
    cout << res[i] << " ";
  }
  return 0;
}
