#include <bits/stdc++.h>
using namespace std;
vector<int> a;
int main() {
  int n, m;
  cin >> n >> m;
  int b[100005];
  for (int i = 0; i < n; i++) scanf("%d", &b[i]);
  sort(b, b + n);
  for (int i = 1, j = 0;; i++) {
    if (i == b[j])
      j++;
    else if (m < i)
      break;
    else
      a.push_back(i), m -= i;
  }
  cout << a.size() << endl;
  for (int i = 0; i < a.size(); i++) printf("%d ", a[i]);
}
