#include <bits/stdc++.h>
using namespace std;
long long n, money, a[100005], k = 0;
vector<long long> ans;
int main() {
  cin >> n >> money;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  for (long long i = 1; i < 10000000000; i++) {
    if (i == a[k]) {
      k++;
      continue;
    }
    if (money - i < 0) break;
    if (money - i >= 0) {
      money -= i;
      ans.push_back(i);
    }
  }
  cout << ans.size() << endl;
  for (long long i = 0; i < ans.size(); i++) cout << ans[i] << " ";
  cout << endl;
  return 0;
}
