#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base ::sync_with_stdio(false);
  cin.tie(NULL);
  int n, k;
  cin >> n >> k;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int i = 1, j = 0;
  queue<int> q;
  while (i <= k) {
    if (j < n) {
      if (a[j] == i)
        j++;
      else {
        q.push(i);
        k -= i;
      }
    } else {
      q.push(i);
      k -= i;
    }
    i++;
  }
  cout << q.size() << endl;
  while (!q.empty()) cout << q.front() << " ", q.pop();
}
