#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<long long> no;
  long long int n, m, s = 0, a[100000], l = 1, i;
  cin >> n >> m;
  for (i = 1; i <= n; i++) cin >> a[i];
  sort(a + 1, a + 1 + n);
  for (i = 1; i <= m; i++) {
    if (a[l] == i)
      l++;
    else {
      s += i;
      if (s <= m)
        no.push_back(i);
      else
        break;
    }
  }
  cout << no.size() << endl;
  for (int j = 0; j < no.size(); j++) cout << no[j] << " ";
  return 0;
}
