#include <bits/stdc++.h>
using namespace std;
int main() {
  set<int> a;
  int n, m, b, i;
  cin >> n >> m;
  vector<int> f;
  for (i = 0; i < n; i++) {
    scanf("%d", &b);
    a.insert(b);
  }
  for (i = 1; m > 0; i++) {
    set<int>::iterator it = a.find(i);
    if (it == a.end()) {
      m = m - i;
      if (m < 0) break;
      f.push_back(i);
    }
  }
  cout << f.size() << "\n";
  for (vector<int>::iterator it = f.begin(); it != f.end(); it++) {
    cout << *it << " ";
  }
  printf("\n");
}
