#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> a;
  vector<int> b;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    a.push_back(x);
  }
  sort(a.begin(), a.end());
  for (int i = 1; i <= 1000000; i++) {
    if (m < i) break;
    if (!binary_search(a.begin(), a.end(), i)) {
      m -= i;
      b.push_back(i);
    }
  }
  cout << b.size() << endl;
  for (int i = 0; i < (int)b.size(); i++) cout << b[i] << " ";
}
