#include <bits/stdc++.h>
using namespace std;
class Solution {
 public:
  void solve(std::istream& in, std::ostream& out) {
    int n, m;
    in >> n >> m;
    unordered_set<int> have;
    while (n--) {
      int a;
      in >> a;
      have.insert(a);
    }
    vector<int> res;
    for (int i = 1; m >= i; ++i) {
      if (!have.count(i)) {
        m -= i;
        res.push_back(i);
      }
    }
    out << res.size() << "\n";
    for (int i : res) out << i << " ";
    out << "\n";
  }
};
void solve(std::istream& in, std::ostream& out) {
  out << std::setprecision(12);
  Solution solution;
  solution.solve(in, out);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  istream& in = cin;
  ostream& out = cout;
  solve(in, out);
  return 0;
}
