#include <bits/stdc++.h>
using namespace std;
bool arr[1100001];
int main() {
  long long int i, count = 0, k, n, m;
  for (i = 0; i < 1100001; i++) arr[i] = false;
  cin >> n >> m;
  for (i = 1; i <= n; i++) {
    cin >> k;
    if (k > 1100000)
      continue;
    else
      arr[k] = true;
  }
  vector<int> vec;
  for (i = 1; i <= 1100001; i++) {
    if (arr[i] == false) {
      m = m - i;
      if (m >= 0) {
        count++;
        vec.push_back(i);
      } else
        break;
    }
  }
  cout << count << endl;
  for (i = 0; i < vec.size(); i++) cout << vec[i] << " ";
  return 0;
}
