#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, x;
  cin >> n >> m;
  set<int> v;
  vector<int> second;
  for (int i = 0; i < n; i++) {
    cin >> x;
    x--;
    v.insert(x);
  }
  int count = 0;
  for (int i = 0; i < 10000000000000; i++) {
    if (v.find(i) != v.end()) continue;
    if (m - i - 1 < 0) break;
    m -= (i + 1);
    count++;
    second.push_back(i + 1);
  }
  cout << count << endl;
  for (int i = 0; i < second.size(); i++) {
    cout << second[i] << " ";
  }
  return 0;
}
