#include <bits/stdc++.h>
using namespace std;
long long arr[1000001];
set<long long> toys_present;
int main() {
  long long n, m;
  cin >> n >> m;
  for (int i = 0; i < n; ++i) {
    int a;
    cin >> a;
    toys_present.insert(a);
  }
  long long money = m;
  vector<int> toys_to_choose;
  int k = 0;
  for (int i = 1; i < 1000000000; ++i) {
    if (toys_present.find(i) == toys_present.end()) {
      if (money >= i) {
        toys_to_choose.push_back(i);
        money -= i;
      } else {
        break;
      }
    }
  }
  cout << toys_to_choose.size() << endl;
  for (int toy : toys_to_choose) {
    cout << toy << " ";
  }
  cout << endl;
}
