#include <bits/stdc++.h>
using ::std::cin;
using ::std::cout;
using ::std::endl;
using ::std::unordered_set;
using ::std::vector;
int main() {
  ::std::ios_base::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  unordered_set<int> toys;
  for (int i = 0; i < n; ++i) {
    int a;
    cin >> a;
    toys.insert(a);
  }
  vector<int> newToys;
  for (int i = 1; i <= m; ++i)
    if (!toys.count(i)) {
      newToys.push_back(i);
      m -= i;
    }
  cout << newToys.size() << endl;
  for (int i : newToys) cout << i << " ";
  cout << endl;
  return 0;
}
