#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m, i;
  cin >> n >> m;
  vector<long long> has;
  long long p;
  for (i = 0; i < n; i++) {
    cin >> p;
    has.push_back(p);
  }
  vector<long long> ans;
  sort(has.begin(), has.end());
  long long j = 0;
  for (i = 1; (i < 200000); i++) {
    if (i != has[j]) {
      m -= i;
      if (m >= 0)
        ans.push_back(i);
      else if (m <= 0)
        break;
    } else
      j++;
    if (m <= 0) break;
  }
  cout << ans.size() << "\n";
  for (i = 0; i < ans.size(); i++) cout << ans[i] << " ";
  return 0;
}
