#include <bits/stdc++.h>
using namespace std;
int n, m, x;
set<int> st;
vector<int> vec;
int main() {
  cin >> n >> m;
  for (long long int i = 1; i <= n; i++) {
    cin >> x;
    st.insert(x);
  }
  int q = 1;
  while (m >= q) {
    if (st.find(q) == st.end()) {
      m -= q;
      vec.push_back(q);
    }
    q++;
  }
  cout << vec.size() << endl;
  if (vec.size())
    for (long long int i = 0; i <= vec.size() - 1; i++) cout << vec[i] << " ";
  return 0;
}
