#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m;
  long long a[100001];
  long long b[100001];
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  long long x = 0, i = 1, count = 0;
  while (m > 0) {
    if (a[x] != i) {
      if (m - i >= 0) {
        m -= i;
        b[count] = i;
        count++;
      } else
        break;
    } else
      x++;
    i++;
  }
  cout << count << endl;
  for (int i = 0; i < count; i++) cout << b[i] << ' ';
}
