#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  long long int m;
  int n;
  cin >> n >> m;
  int t;
  set<long long int> toys;
  vector<long long int> out;
  for (int i = 0; i < n; i++) {
    cin >> t;
    toys.insert(t);
  }
  for (int i = 1; i < 1e9; i++) {
    if (toys.find(i) == toys.end()) {
      if (m >= i) {
        m -= i;
        out.push_back(i);
      } else
        break;
    }
  }
  cout << out.size() << endl;
  for (int i = 0; i < out.size(); i++) {
    cout << out[i] << " ";
  }
  cout << endl;
}
