#include <bits/stdc++.h>
using namespace std;
int n, sum, x;
set<int> s;
vector<int> v;
vector<int>::iterator it;
int main() {
  cin >> n >> sum;
  for (int i = 1; i <= n; i++) {
    cin >> x;
    s.insert(x);
  }
  int k = 0;
  while (sum >= 0) {
    k++;
    if (s.find(k) != s.end()) {
      ;
    } else {
      sum = sum - k;
      v.push_back(k);
    }
  }
  cout << v.size() - 1 << '\n';
  for (int i = 0; i < v.size() - 1; i++) {
    cout << v[i] << " ";
  }
  return 0;
}
