#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int i, count = 0, k, n, m;
  cin >> n >> m;
  vector<int> vec, v;
  for (i = 0; i < n; i++) {
    cin >> k;
    vec.push_back(k);
  }
  sort(vec.begin(), vec.end());
  for (i = 1;; i++) {
    if (!binary_search(vec.begin(), vec.end(), i)) {
      m = m - i;
      if (m >= 0) {
        count++;
        v.push_back(i);
      } else
        break;
    }
  }
  cout << count << endl;
  for (i = 0; i < v.size(); i++) cout << v[i] << " ";
  cout << endl;
  return 0;
}
