#include <bits/stdc++.h>
using namespace std;
int n, m, i, k, c, x;
vector<int> v;
map<int, int> mp;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> x;
    mp[x] = 1;
  }
  i = 1;
  while (c + i <= m) {
    if (mp[i] == 0) {
      c += i;
      v.push_back(i);
      k++;
    }
    i++;
  }
  cout << k << endl;
  for (int i = 0; i < k; i++) cout << v[i] << ' ';
}
