#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  map<int, bool> a;
  for (int i = 0, j; i < n; i++) {
    cin >> j;
    a[j] = 1;
  }
  int k = 0;
  vector<int> l;
  for (int i = 1; m - i >= 0; i++)
    if (!a[i]) {
      l.push_back(i);
      m -= i;
    }
  cout << l.size() << endl;
  for (int i = 0; i < l.size(); i++) cout << l[i] << ' ';
}
