#include <bits/stdc++.h>
using namespace std;
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  map<long long int, long long int> m;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    m[x]++;
  }
  long long int sum = 0, count = 0;
  string s;
  for (long long int i = 1; i < 10e9; i++) {
    if (m[i] > 0) continue;
    if (sum + i > k) break;
    sum += i;
    stringstream ss;
    ss << i;
    string str = ss.str();
    s += str + " ";
    count++;
  }
  cout << count << endl;
  cout << s << endl;
}
