#include <bits/stdc++.h>
using namespace std;
const long long MAX = 1e6;
long long power(long long a, long long b, long long m) {
  long long r = 1;
  while (b) {
    if (b % 2 == 1) r = (r * a) % m;
    b /= 2;
    a = (a * a) % m;
  }
  return r;
}
bool prime[MAX];
void sieve(long long n) {
  memset(prime, true, sizeof(prime));
  for (long long p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (long long i = p * 2; i <= n; i += p) prime[i] = false;
    }
  }
}
map<long long, long long> pfactors;
void pfact(long long n) {
  for (long long i = 2; i <= sqrt(n); i++) {
    if (n % i == 0) {
      while (n % i == 0) {
        pfactors[i]++;
        n /= i;
      }
    }
  }
  if (n > 1) pfactors[n]++;
  for (auto it : pfactors) {
    cout << it.first << " -> " << it.second << "\n";
  }
}
void solve() {
  long long n, k;
  cin >> n >> k;
  set<long long> st;
  for (long long i = 0; i < n; ++i) {
    long long x;
    cin >> x;
    st.insert(x);
  }
  long long ans = 0;
  vector<long long> vp;
  for (long long i = 1; i <= k; i++) {
    if (i > k) break;
    if (st.find(i) == st.end()) {
      k -= i;
      ans++;
      vp.push_back(i);
    }
  }
  cout << ans << "\n";
  for (auto it : vp) {
    cout << it << " ";
  }
}
int main() {
  solve();
  return 0;
}
