#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m;
  cin >> n >> m;
  vector<long long> a(n);
  map<int, int> mp;
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    mp[a[i]] = 1;
  }
  long long s = 0, c = 0;
  vector<long long> ans;
  for (long long i = 1; s < m; i++) {
    if (mp[i] != 1 && s + i <= m) {
      ans.push_back(i);
      s += i;
      c++;
    }
    if (s + i > m) {
      break;
    }
  }
  cout << c << endl;
  for (long long i = 0; i < ans.size(); i++) {
    cout << ans[i] << " ";
  }
  cout << endl;
  return 0;
}
