#include <bits/stdc++.h>
using namespace std;
map<int, bool> a;
vector<int> ans;
int main() {
  ios_base::sync_with_stdio(0);
  int n, m, b;
  cin >> n >> m;
  for (int i = 1; i <= n; i++) {
    cin >> b;
    a[b] = 1;
  }
  for (int i = 1;; i++) {
    if (i > m) break;
    if (a[i] == 0) {
      ans.push_back(i);
      m -= i;
    }
  }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++) cout << ans[i] << " ";
  return 0;
}
