#include <bits/stdc++.h>
using namespace std;
int used[200050];
int main() {
  int n, k, cnt = 0, sum = 0, x;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    cin >> x;
    if (x <= 200000) used[x] = true;
  }
  for (int i = 1; i <= k; i++) {
    if (used[i] == false) {
      cnt++;
      sum += i;
      if (sum > k) {
        cnt--;
        break;
      }
      if (sum == k) break;
    }
  }
  sum = 0;
  cout << cnt << endl;
  for (int i = 1; i <= k; i++) {
    if (used[i] == false) {
      sum += i;
      if (sum > k)
        break;
      else
        cout << i << " ";
    }
  }
  return 0;
}
