#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n, m;
  cin >> n >> m;
  vector<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a.begin(), a.end());
  vector<int> ans;
  int budget = m;
  for (int i = 1; i <= m; i++) {
    if (binary_search(a.begin(), a.end(), i)) continue;
    if (budget >= i) {
      budget = budget - i;
      ans.push_back(i);
    } else
      break;
  }
  int l = ans.size();
  cout << l << "\n";
  for (int i = 0; i < l; i++) cout << ans[i] << " ";
  cout << "\n";
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  solve();
}
