#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int arr[n];
  vector<int> mm;
  for (int i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  int s = 1;
  bool ok = true;
  for (int i = 0; i < n; i++) {
    if (ok == false) break;
    if (s == arr[i]) {
      s++;
    } else {
      while (s != arr[i]) {
        if (s <= m) {
          mm.push_back(s);
          m -= s;
          s++;
        } else {
          ok = false;
          break;
        }
      }
      s++;
    }
  }
  while (ok) {
    if (s <= m) {
      mm.push_back(s);
      m -= s;
      s++;
    } else {
      ok = false;
      break;
    }
  }
  cout << mm.size() << endl;
  for (int i = 0; i < mm.size(); i++) cout << mm[i] << " ";
}
