#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  long long m;
  cin >> n >> m;
  vector<int> ans;
  set<int> existingToys;
  for (int i = 0; i < n; i++) {
    int idx;
    cin >> idx;
    existingToys.insert(idx);
  }
  for (int i = 1; i <= m; i++) {
    if (existingToys.find(i) != existingToys.end())
      continue;
    else {
      m -= i;
      ans.push_back(i);
    }
  }
  cout << ans.size() << endl;
  for (auto x : ans) cout << x << " ";
  cout << endl;
  return 0;
}
