description: This is an easier version of the problem with smaller constraints.
  
  Korney Korneevich dag up an array a of length n. Korney Korneevich has recently read about the operation [bitwise XOR](https://en.wikipedia.org/wiki/Bitwise_operation#XOR), so he wished to experiment with it. For this purpose, he decided to find all integers x ≥ 0 such that there exists an increasing subsequence of the array a, in which the bitwise XOR of numbers is equal to x.
  
  It didn't take a long time for Korney Korneevich to find all such x, and he wants to check his result. That's why he asked you to solve this problem!
  
  A sequence s is a subsequence of a sequence b if s can be obtained from b by deletion of several (possibly, zero or all) elements.
  
  A sequence s_1, s_2, … , s_m is called increasing if s_1 < s_2 < … < s_m.
  
  Input
  
  The first line contains a single integer n (1 ≤ n ≤ 10^5).
  
  The second line contains n integers a_1, a_2, …, a_n (0 ≤ a_i ≤ 500) — the elements of the array a.
  
  Output
  
  In the first line print a single integer k — the number of found x values.
  
  In the second line print k integers in increasing order x_1, x_2, … x_k (0 ≤ x_1 < … < x_k) — found x values.
  
  Examples
  
  Input
  
  
  4
  4 2 2 4
  
  
  Output
  
  
  4
  0 2 4 6 
  
  
  Input
  
  
  8
  1 0 1 7 12 5 3 2
  
  
  Output
  
  
  12
  0 1 2 3 4 5 6 7 10 11 12 13 
  
  Note
  
  In the first test case:
  
    * To get value x = 0 it is possible to choose and empty subsequence 
    * To get value x = 2 it is possible to choose a subsequence [2] 
    * To get value x = 4 it is possible to choose a subsequence [4] 
    * To get value x = 6 it is possible to choose a subsequence [2, 4] 
solution: import java.util.*;
  import java.io.*;
  
  public class MyClass {
      
      private static int M = 512;
      
      public static void main(String args[]) throws Exception {
        BufferedReader s = new BufferedReader(new InputStreamReader(System.in));
        
        
        int n = Integer.parseInt(s.readLine());
        int[] a = new int[n];
        
        String[] ss = s.readLine().split(" ");
        for (int i = 0; i < n; ++i) {
            a[i] = Integer.parseInt(ss[i]);
        }
        
        int[] mp = new int[M + 5];
        int[] mpt = new int[M + 5];
        
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j <= M + 2; ++j) {
                mpt[j] = mp[j];
            }
            
            if (mp[a[i]] > 0 && mp[a[i]] > a[i] || mp[a[i]] == 0) {
                mpt[a[i]] = a[i];
            }
            
            for (int x = 0; x <= M + 2; ++x) 
              if (mp[x] > 0) {
                  if (mp[x] < a[i]) {
                      int z = x ^ a[i];
                      if (mp[z] == 0 || mp[z] > a[i]) {
                          mpt[z] = a[i];
                      }
                  }
              }
            
            for (int j = 0; j <= M + 2; ++j) {
                mp[j] = mpt[j];
            }
        }
        
        int res = 1;
        for (int i = 1; i <= M + 2; ++i) 
          if (mp[i] > 0) {
              res++;
          }
        System.out.println(res);
        System.out.print(0);
        for (int i = 1; i <= M + 2; ++i) 
          if (mp[i] > 0) {
                System.out.print(" " + i);
          }
          
        System.out.println();
      }
  }