#include <bits/stdc++.h>
using namespace std;
long long n, m, x, ant, N = 300005;
bool pos[300005];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> m;
  vector<long long> ans;
  for (int i = 0; i < n; i++) {
    cin >> x;
    if (x < N) pos[x] = true;
  }
  for (int i = 1; i <= N; ++i) {
    if (!pos[i]) {
      if (i > m) break;
      m -= i;
      ans.push_back(i);
    }
  }
  cout << (int)ans.size() << "\n";
  for (int i = 0; i < (int)ans.size(); ++i) {
    cout << ans[i];
    if (i + 1 < (int)ans.size()) cout << " ";
  }
  cout << "\n";
  return 0;
}
