#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, m, k = 0, e, mo = 0, d, i, l = -8909, j = -987, na = 0,
                      p = 0, o = 1, t = 0, z = 0;
  cin >> n >> m;
  long long int a[n], b[99999];
  for (i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  for (i = 1, j = 0, k = 0;; i++) {
    if (n > j) {
      if (i == a[j]) {
        j++;
        continue;
      }
    }
    m = m - i;
    if (m >= 0) {
      b[k] = i;
      k++;
    } else
      break;
  }
  cout << k << endl;
  for (i = 0; i < k; i++) {
    cout << b[i] << " ";
  }
  return 0;
}
