#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m, x;
  cin >> n >> m;
  vector<long long> v;
  map<long long, int> ma;
  for (int i = 0; i < n; i++) {
    cin >> x;
    ma.insert(pair<long long, int>(x, 1));
  }
  for (int i = 1; i <= 1000000000; i++) {
    if (m < i)
      break;
    else {
      if (ma[i] != 1 && m - i >= 0) {
        v.push_back(i);
        m -= i;
      }
    }
  }
  cout << v.size() << endl;
  for (int i = 0; i < v.size(); i++) cout << v[i] << " ";
}
