#include <bits/stdc++.h>
using namespace std;
const long long INF = 1LL << 50LL;
const double PI = 3.14159265358979323846264;
int main() {
  long long n, m;
  cin >> n >> m;
  set<long long> a;
  for (int i = 0; i < n; i++) {
    long long v;
    cin >> v;
    a.insert(v);
  }
  vector<long long> ans;
  for (long long i = 1; i <= m; i++) {
    if (a.find(i) != a.end()) continue;
    ans.push_back(i);
    m -= i;
  }
  cout << ans.size() << endl;
  if (!ans.empty()) {
    for (int i = 0; i < ans.size() - 1; i++) cout << ans[i] << " ";
    cout << ans.back() << endl;
  }
  return 0;
}
