#include <bits/stdc++.h>
using namespace std;
const long long inf = LONG_MAX;
const long long arr = 1000000;
bool comp(pair<string, long long> a, pair<string, long long> b) {
  if (a.second == b.second)
    return a.first < b.first;
  else
    return a.second > b.second;
}
int main(void) {
  long long n, m;
  cin >> n >> m;
  map<long long, long long> make_pair;
  for (int i = 0; i < n; i++) {
    long long x;
    cin >> x;
    make_pair[x] = 1;
  }
  long long sum = 0;
  vector<long long> v;
  for (long long i = 1; i <= LLONG_MAX; i++) {
    if (sum >= m) break;
    if (make_pair[i] == 0) {
      if (sum + i <= m) {
        sum += i;
        v.push_back(i);
      } else
        break;
    }
  }
  cout << v.size() << '\n';
  for (auto first : v) cout << first << " ";
  return 0;
}
