#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, num;
  cin >> n >> m;
  vector<int> ans;
  set<int> S;
  for (int i = 0; i < n; ++i) {
    cin >> num;
    S.insert(num);
  }
  for (int i = 1; i <= m; ++i)
    if (S.find(i) == S.end()) {
      ans.push_back(i);
      m -= i;
    }
  cout << ans.size() << '\n';
  for (int i = 0; i < ans.size(); ++i) cout << ans[i] << " ";
  cout << '\n';
}
