#include <bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[]) {
  int n, count;
  cin >> n >> count;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  vector<int> ans;
  int iter = 1, track = 0;
  const int size = 1e9;
  while (iter < size && (count - iter >= 0)) {
    if (track < n && iter == arr[track]) {
      track++;
      iter++;
      continue;
    }
    count = count - iter;
    ans.push_back(iter);
    iter++;
  }
  cout << ans.size() << endl;
  for (int i; i < ans.size(); i++) cout << ans[i] << " ";
  cout << endl;
  return 0;
}
