#include <bits/stdc++.h>
using namespace std;
long long n, m;
set<long long> t;
vector<long long> ans;
int main() {
  cin >> n >> m;
  for (long long i = 0; i < n; i++) {
    long long a;
    cin >> a;
    t.insert(a);
  }
  for (long long i = 1; i <= m; i++) {
    if (!t.count(i)) {
      m -= i;
      ans.push_back(i);
    }
  }
  cout << ans.size() << endl;
  for (long long i = 0; i < ans.size(); i++) {
    cout << ans[i] << " ";
  }
}
