#include <bits/stdc++.h>
using namespace std;
vector<int> toys;
set<int> t;
set<int>::iterator it;
int main() {
  int n, k;
  cin >> n >> k;
  int x;
  for (int i = 0; i < n; i++) {
    cin >> x;
    t.insert(x);
  }
  int i = 1;
  int sum = 0;
  while (k >= 0) {
    it = t.find(i);
    if (it == t.end()) {
      k -= i;
      sum++;
      toys.push_back(i);
      i++;
    } else
      i++;
  }
  sum--;
  toys.pop_back();
  cout << sum << '\n';
  for (int i = 0; i < toys.size(); i++) cout << toys[i] << " ";
}
