#include <bits/stdc++.h>
using namespace std;
int toy[100016];
int ans[100016];
int main() {
  int n, m, acnt = 0;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> toy[i];
  }
  sort(toy, toy + n);
  for (int i = 1; i <= 1000000000; i++) {
    if (!binary_search(toy, toy + n, i)) {
      if (m >= i) {
        m -= i;
        ans[acnt] = i;
        acnt++;
      } else
        break;
    }
  }
  cout << acnt << endl;
  for (int i = 0; i < acnt; i++) {
    cout << ans[i] << " ";
  }
  return 0;
}
