#include <bits/stdc++.h>
using namespace std;
template <class T1>
void deb(T1 e1) {
  cout << e1 << endl;
}
template <class T1, class T2>
void deb(T1 e1, T2 e2) {
  cout << e1 << " " << e2 << endl;
}
template <class T1, class T2, class T3>
void deb(T1 e1, T2 e2, T3 e3) {
  cout << e1 << " " << e2 << " " << e3 << endl;
}
template <class T1, class T2, class T3, class T4>
void deb(T1 e1, T2 e2, T3 e3, T4 e4) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << endl;
}
template <class T1, class T2, class T3, class T4, class T5>
void deb(T1 e1, T2 e2, T3 e3, T4 e4, T5 e5) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << " " << e5 << endl;
}
template <class T1, class T2, class T3, class T4, class T5, class T6>
void deb(T1 e1, T2 e2, T3 e3, T4 e4, T5 e5, T6 e6) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << " " << e5 << " " << e6
       << endl;
}
int main() {
  long long n, m, x, y, sum = 0, total;
  vector<long> v, v1, v2;
  set<int> s, s1, s2;
  map<long long, bool> Mymap;
  scanf("%I64d %I64d", &n, &m);
  for (long long int i = 1; i <= n; i++) {
    cin >> x;
    Mymap[x]++;
  }
  for (long long int j = 1; j <= m; j++) {
    if (Mymap[j] != true) {
      m -= j;
      v.push_back(j);
    }
  }
  cout << v.size() << endl;
  for (auto it : v) {
    cout << it << " ";
  }
  cout << endl;
  v.clear();
  Mymap.clear();
  return 0;
}
