#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  map<int, bool> mp;
  for (int i = 0; i < n; i++) {
    int x;
    scanf("%d", &x);
    mp[x] = true;
  }
  vector<int> v;
  for (int i = 1;; i++) {
    if (mp[i] == true) continue;
    if (m >= i) {
      v.push_back(i);
      m -= i;
    } else
      break;
  }
  printf("%d\n", v.size());
  for (int i = 0; i < v.size(); i++) {
    printf("%d ", v[i]);
  }
  printf("\n");
  return 0;
}
