#include <bits/stdc++.h>
using namespace std;
int main() {
  cin.tie(0);
  std::ios::sync_with_stdio(false);
  long long n, sum, temp, i;
  cin >> n >> sum;
  map<long long, long long> m;
  for (i = 0; i < n; i++) {
    cin >> temp;
    m[temp] = 1;
  }
  vector<long long> v;
  long long newsum = 0;
  for (i = 1; i <= 1000000000; i++) {
    if (m[i] == 0) {
      newsum += i;
      if (newsum > sum) {
        newsum -= i;
        break;
      }
      v.push_back(i);
      m[i] = 1;
    }
  }
  cout << v.size() << endl;
  for (i = 0; i < v.size(); i++) {
    cout << v[i] << " ";
  }
  cout << endl;
  return 0;
}
