#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int n, m, arr[100005];
  vector<int> temp;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  int sum = 0;
  for (int i = 1;; i++) {
    if (!binary_search(arr, arr + n, i)) {
      sum += i;
      if (sum > m) break;
      temp.push_back(i);
    }
  }
  cout << temp.size() << endl;
  for (int i = 0; i < temp.size(); i++) {
    cout << temp[i] << " ";
  }
  cout << endl;
  return 0;
}
