#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int a[n];
  map<int, bool> mp;
  vector<int> v;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    mp[a[i]] = true;
  }
  int c = 0;
  for (int i = 1; i < 1000000000 + 1; i++) {
    map<int, bool>::iterator it;
    if (m < i) break;
    it = mp.find(i);
    if (it != mp.end()) continue;
    c++;
    m -= i;
    v.push_back(i);
  }
  cout << c << endl;
  for (int i = 0; i < v.size(); i++) cout << v[i] << " ";
  cout << endl;
  return 0;
}
