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