#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  map<int, bool> mp;
  vector<int> v;
  int arr[100000], cnt = 0, sum = 0;
  int ans;
  for (int i = 1; i <= n; i++) {
    cin >> arr[i];
    mp[arr[i]] = true;
  }
  int i = 1;
  while (k >= i) {
    if (!mp[i]) k -= i, v.push_back(i);
    i++;
  }
  cout << v.size() << "\n";
  for (int i = 0; i < v.size(); i++) cout << v[i] << " ";
  return 0;
}
