#include <bits/stdc++.h>
using namespace std;
const long long inf = LLONG_MAX / 2;
const long long MX = 1e5 + 10;
int a[MX];
set<int> s;
vector<int> v;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, m;
  cin >> n >> m;
  for (long long(i) = (0); (i) <= (n - 1); ++(i)) {
    cin >> a[i];
    s.insert(a[i]);
  }
  int num = 1;
  while (m >= num) {
    if (!s.count(num)) {
      m -= num;
      v.push_back(num);
    }
    num++;
  }
  cout << v.size() << endl;
  for (auto it : v) {
    cout << it << " ";
  }
  return 0;
}
