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.io.*;
  import java.util.*;
  
  public class CodeForces{
      /*-------------------------------------------EDITING CODE STARTS HERE-------------------------------------------*/
      public static void main(String[] args) throws IOException{
          openIO();
          int testCase = 1;
  //        testCase = sc.nextInt();
          preCompute();
          for (int i = 1; i <= testCase; i++) solve(i);
          closeIO();
      }
  
      public static void solve(int tCase)throws IOException {
          int n = sc.nextInt();
          int[] arr =  new int[n];
          for(int i=0;i<n;i++)arr[i] = sc.nextInt();
          int[] dp = new int[513];
          int mx = 2000;
          Arrays.fill(dp,mx);
          dp[0] =  -10;
          for(int i=0;i<n;i++){
              for(int j = 512;j>=0;j--){
                  if(dp[j] != mx && arr[i] > dp[j]){
                      int curr = j ^ arr[i];
                      if(curr >j && curr<513)dp[curr] = Math.min(dp[curr],arr[i]);
                  }
              }
              for(int j = 0;j<=512;j++){
                  if(dp[j] != mx && arr[i] > dp[j]){
                      int curr = j ^ arr[i];
                      if(curr <j)dp[curr] = Math.min(dp[curr],arr[i]);
                  }
              }
          }
          List<Integer> ans = new ArrayList<>();
          for(int i=0;i<513;i++)
              if(dp[i]!=mx)ans.add(i);
          out.println(ans.size());
          for(int ele : ans)out.print(ele+" ");
      }
  
      private static void  preCompute(){
  
      }
      /*-------------------------------------------EDITING CODE ENDS HERE-------------------------------------------*/
      static FastestReader sc;
      static PrintWriter out;
      private static void openIO() throws IOException{
          sc = new FastestReader();
          out = new PrintWriter(System.out);
      }
  
      /*------------------------------------------HELPER FUNCTION STARTS HERE------------------------------------------*/
  
      public static final int mod = (int) 1e9 +7;
      private static final int mod2 =  998244353;
      public static final int inf_int = (int) 2e9;
      public static  final long inf_long = (long) 2e18;
  
      // euclidean algorithm time O(max (loga ,logb))
      public static long _gcd(long a, long b) {
          long x = Math.min(a, b);
          long y = Math.max(a, b);
          if (y % x == 0) return x;
          return _gcd(y % x, x);
      }
  
      public static long _lcm(long a, long b) {
          // lcm(a,b) * gcd(a,b) = a * b
          return (a / _gcd(a, b)) * b;
      }
      // binary exponentiation time O(logn)
      public static long _power(long x, long n) {
          long ans = 1;
          while (n > 0) {
              if ((n & 1) == 1) {
                  ans *= x;
                  ans %= mod;
                  n--;
              } else {
                  x *= x;
                  x %= mod;
                  n >>= 1;
              }
          }
          return ans;
      }
      //sieve/first divisor time : O(mx * log ( log (mx) ) )
      public static int[]  _seive(int mx){
          int[] firstDivisor = new int[mx+1];
          for(int i=0;i<=mx;i++)firstDivisor[i] = i;
          for(int i=2;i*i<=mx;i++)
              if(firstDivisor[i] == i)
                  for(int j = i*i;j<=mx;j+=i)
                      firstDivisor[j] = i;
          return firstDivisor;
      }
  
      private static boolean isPrime(long x){
          for(long i=2;i*i<=x;i++)
              if(x%i==0)return false;
          return true;
      }
  
  
      /*------------------------------------------HELPER FUNCTION ENDS HERE-------------------------------------------*/
  
      /*-------------------------------------------FAST INPUT STARTS HERE---------------------------------------------*/
  
      public static void closeIO() throws IOException{
          out.flush();
          out.close();
          sc.close();
      }
      private static final class FastestReader {
          private static final int BUFFER_SIZE = 1 << 16;
          private final DataInputStream din;
          private final byte[] buffer;
          private int bufferPointer, bytesRead;
  
          public FastestReader() {
              din = new DataInputStream(System.in);
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public FastestReader(String file_name) throws IOException {
              din = new DataInputStream(new FileInputStream(file_name));
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          private static boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
  
          private int skip() throws IOException {
              int b;
              //noinspection StatementWithEmptyBody
              while ((b = read()) != -1 && isSpaceChar(b)) {}
              return b;
          }
  
          public String next() throws IOException {
              int b = skip();
              final StringBuilder sb = new StringBuilder();
              while (!isSpaceChar(b)) { // when nextLine, (isSpaceChar(b) && b != ' ')
                  sb.appendCodePoint(b);
                  b = read();
              }
              return sb.toString();
          }
  
          public int nextInt() throws IOException {
              int ret = 0;
              byte c = read();
              while (c <= ' ') {
                  c = read();
              }
              final 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(); }
              final 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(); }
              final 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 {
              din.close();
          }
      }
      /*---------------------------------------------FAST INPUT ENDS HERE ---------------------------------------------*/
  }