#include <bits/stdc++.h>
using namespace std;
const int N = 100100;
long long n, t[N], m, res, ans[N];
int dd[N];
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> m;
  for (int i = 1; i <= n; i++) cin >> t[i];
  sort(t + 1, t + n + 1);
  long long sum = 0;
  int j = 1;
  for (int i = 1; i <= 200000; i++) {
    if (sum + i > m) {
      res = i - 1;
      break;
    }
    if (j <= n && t[j] == i)
      j++;
    else
      sum += i;
  }
  int dem = 0;
  j = 1;
  for (int i = 1; i <= res; i++) {
    if (j > n || i != t[j]) {
      dem++;
      ans[dem] = i;
    } else
      j++;
  }
  cout << dem << endl;
  for (int i = 1; i <= dem; i++) cout << ans[i] << " ";
  return 0;
}
