#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  long long m, toy;
  map<long long, long long> type;
  vector<long long> ve;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> toy;
    type[toy]++;
  }
  for (long long i = 1;; i++) {
    if (type[i] == 0 && m - i >= 0) {
      m -= i;
      ve.push_back(i);
    }
    if (m - i <= 0) break;
  }
  int len = ve.size();
  cout << len << endl;
  for (int i = 0; i < len; i++) cout << ve[i] << " ";
  cout << endl;
}
