#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, j = 0, n, m, ans = 0, k = 0;
  cin >> n >> m;
  int has[n];
  int print[44721];
  for (i = 0; i < n; i++) {
    cin >> has[i];
  }
  sort(has, has + n);
  i = 1;
  while (1) {
    if (m < i) {
      break;
    }
    if (i != has[j] && m >= i) {
      ans++;
      print[k] = i;
      k++;
      m = m - i;
      i++;
      continue;
    } else if (i == has[j] && m >= i) {
      i++;
      j++;
      continue;
    }
  }
  cout << ans << '\n';
  for (i = 0; i < ans; i++) {
    cout << print[i] << " ";
  }
  return 0;
}
