#include <bits/stdc++.h>
using namespace std;
int main() {
  bool a[1000001];
  int n, m;
  vector<int> vec;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) {
    int c;
    scanf("%d", &c);
    if (c > 1000000) continue;
    a[c] = true;
  }
  for (int i = 1; i <= m && m >= 0; i++) {
    if (a[i]) continue;
    vec.push_back(i);
    m -= i;
  }
  cout << vec.size() << endl;
  for (int i = 0; i < vec.size(); i++) printf("%d ", vec[i]);
  return 0;
}
