#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  long long int n, m, i, a, counter = 0;
  cin >> n >> m;
  map<long long int, int> mapper;
  for (i = 0; i < n; i++) {
    cin >> a;
    mapper[a]++;
  }
  long long sum = 0;
  for (i = 1;; i++) {
    if (mapper[i] == 0) {
      sum += i;
      counter++;
    }
    if (sum > m) {
      counter--;
      break;
    }
  }
  cout << counter << endl;
  sum = 0;
  for (i = 1;; i++) {
    if (mapper[i] == 0) sum += i;
    if (sum > m)
      break;
    else if (mapper[i] == 0 && sum == i)
      cout << i;
    else if (mapper[i] == 0)
      cout << " " << i;
  }
}
