#include <bits/stdc++.h>
using namespace std;
map<int, bool> has;
vector<int> bag;
int main() {
  unsigned long long n, m, h;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> h;
    has[h] = true;
  }
  unsigned long long sum = 0, giftNo = 1;
  while (sum < m) {
    if (has.find(giftNo) == has.end()) {
      sum += giftNo;
      if (sum > m) break;
      bag.push_back(giftNo);
      has[giftNo] = true;
    }
    giftNo++;
  }
  cout << bag.size() << endl;
  for (int i = 0; i < bag.size(); i++) {
    cout << bag[i] << " ";
  }
  cout << endl;
  return 0;
}
