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: //package Codeforces.Round750Div2;
  
  import java.io.*;
  import java.util.*;
  
  public class F1 {
      public static void main(String[] args) throws IOException {
          Soumit sc = new Soumit();
  
          int n = sc.nextInt();
          int[] arr = sc.nextIntArray(n);
          StringBuilder sb = new StringBuilder();
  
          int[] hash = new int[1500];
          Arrays.fill(hash, 1000);
          hash[0] = 0;
  
          Set<Integer> set = new HashSet<>();
          set.add(0);
          for(int i=0;i<n;i++){
              int v = arr[i];
              for(int j=0;j<hash.length;j++){
                  if(hash[j]<v){
                      set.add(j^v);
                      hash[j^v] = Math.min(hash[j^v], v);
                  }
              }
          }
  
          ArrayList<Integer> arlist = new ArrayList<>(set);
          Collections.sort(arlist);
  
          sb.append(arlist.size()).append("\n");
          for(int i: arlist){
              sb.append(i).append(" ");
          }
  
          System.out.println(sb);
  
          sc.close();
      }
  
      static class Soumit {
          final private int BUFFER_SIZE = 1 << 18;
          final private DataInputStream din;
          final private byte[] buffer;
          private PrintWriter pw;
          private int bufferPointer, bytesRead;
          StringTokenizer st;
  
          public Soumit() {
              din = new DataInputStream(System.in);
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public Soumit(String file_name) throws IOException {
              din = new DataInputStream(new FileInputStream(file_name));
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public void streamOutput(String file) throws IOException {
              FileWriter fw = new FileWriter(file);
              BufferedWriter bw = new BufferedWriter(fw);
              pw = new PrintWriter(bw);
          }
  
          public void println(String a) {
              pw.println(a);
          }
  
          public void print(String a) {
              pw.print(a);
          }
  
          public String readLine() throws IOException {
              byte[] buf = new byte[3000064]; // line length
              int cnt = 0, c;
              while ((c = read()) != -1) {
                  if (c == '\n')
                      break;
                  buf[cnt++] = (byte) c;
              }
              return new String(buf, 0, cnt);
          }
  
          String next() {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
  
          public void sort(int[] arr) {
              ArrayList<Integer> arlist = new ArrayList<>();
              for (int i : arr)
                  arlist.add(i);
  
              Collections.sort(arlist);
              for (int i = 0; i < arr.length; i++)
                  arr[i] = arlist.get(i);
          }
  
          public void sort(long[] arr) {
              ArrayList<Long> arlist = new ArrayList<>();
              for (long i : arr)
                  arlist.add(i);
  
              Collections.sort(arlist);
              for (int i = 0; i < arr.length; i++)
                  arr[i] = arlist.get(i);
          }
  
          public int[] nextIntArray(int n) throws IOException {
              int[] arr = new int[n];
              for (int i = 0; i < n; i++) {
                  arr[i] = nextInt();
              }
  
              return arr;
          }
  
          public long[] nextLongArray(int n) throws IOException {
              long[] arr = new long[n];
              for (int i = 0; i < n; i++) {
                  arr[i] = nextLong();
              }
  
              return arr;
          }
  
          public double[] nextDoubleArray(int n) throws IOException {
              double[] arr = new double[n];
              for (int i = 0; i < n; i++) {
                  arr[i] = nextDouble();
              }
  
              return arr;
          }
  
          public int nextInt() throws IOException {
              int ret = 0;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          public long nextLong() throws IOException {
              long ret = 0;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              }
              while ((c = read()) >= '0' && c <= '9');
              if (neg)
                  return -ret;
              return ret;
          }
  
          public double nextDouble() throws IOException {
              double ret = 0, div = 1;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
  
              do {
                  ret = ret * 10 + c - '0';
              }
              while ((c = read()) >= '0' && c <= '9');
  
              if (c == '.') {
                  while ((c = read()) >= '0' && c <= '9') {
                      ret += (c - '0') / (div *= 10);
                  }
              }
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          private void fillBuffer() throws IOException {
              bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
              if (bytesRead == -1)
                  buffer[0] = -1;
          }
  
          private byte read() throws IOException {
              if (bufferPointer == bytesRead)
                  fillBuffer();
              return buffer[bufferPointer++];
          }
  
          public void close() throws IOException {
              /*if (din == null)
                  return;*/
              if (din != null) din.close();
              if (pw != null) pw.close();
          }
      }
  }
  