#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  int a;
  set<int> s, r;
  for (int x = 0; x < n; ++x) {
    scanf("%d", &a);
    s.insert(a);
  }
  for (int x = 1; x <= 1000000000; ++x) {
    if (s.find(x) == s.end()) {
      if (m >= x) {
        m -= x;
        r.insert(x);
      } else {
        break;
      }
    }
  }
  cout << r.size() << endl;
  for (auto x : r) {
    printf("%d ", x);
  }
  cout << endl;
  return 0;
}
