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.ByteArrayInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.InputMismatchException;
  import java.util.List;
  
  public class Main {
  
  	private static final String NO = "No";
  	private static final String YES = "Yes";
  	InputStream is;
  	PrintWriter out;
  	String INPUT = "";
  
  	private static final int MOD = 998244353;
  
  	void solve() {
  		int T = 1;// ni();
  		for (int i = 0; i < T; i++)
  			solve(i);
  	}
  
  	void solve(int ic) {
  		int n = ni();
  		int b[] = new int[512];
  		Arrays.fill(b, Integer.MAX_VALUE);
  		b[0] = 0;
  		for (int i = 1; i <= n; i++) {
  			int k = ni();
  			b[k] = Math.min(b[k], k);
  			for (int j = 1; j < b.length; j++)
  				if (b[j] >= 0 && b[j] < k) {
  					b[j ^ k] = Math.min(b[j ^ k], k);
  				}
  		}
  
  		int cnt = 0;
  		for (int i = 0; i < b.length; i++)
  			if (b[i] != Integer.MAX_VALUE)
  				cnt++;
  		out.println(cnt);
  		for (int i = 0; i < b.length; i++)
  			if (b[i] != Integer.MAX_VALUE)
  				out.print(i + " ");
  	}
  
  	// a^b
  	long power(long a, long b) {
  		long x = 1, y = a;
  		while (b > 0) {
  			if (b % 2 != 0) {
  				x = (x * y) % MOD;
  			}
  			y = (y * y) % MOD;
  			b /= 2;
  		}
  		return x % MOD;
  	}
  
  	private long gcd(long a, long b) {
  		while (a != 0) {
  			long tmp = b % a;
  			b = a;
  			a = tmp;
  		}
  		return b;
  	}
  
  	void run() throws Exception {
  		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
  		out = new PrintWriter(System.out);
  
  		long s = System.currentTimeMillis();
  		solve();
  		out.flush();
  		if (!INPUT.isEmpty())
  			tr(System.currentTimeMillis() - s + "ms");
  	}
  
  	public static void main(String[] args) throws Exception {
  		new Main().run();
  	}
  
  	private byte[] inbuf = new byte[1024];
  	public int lenbuf = 0, ptrbuf = 0;
  
  	private int readByte() {
  		if (lenbuf == -1)
  			throw new InputMismatchException();
  		if (ptrbuf >= lenbuf) {
  			ptrbuf = 0;
  			try {
  				lenbuf = is.read(inbuf);
  			} catch (IOException e) {
  				throw new InputMismatchException();
  			}
  			if (lenbuf <= 0)
  				return -1;
  		}
  		return inbuf[ptrbuf++];
  	}
  
  	private boolean isSpaceChar(int c) {
  		return !(c >= 33 && c <= 126);
  	}
  
  	private int skip() {
  		int b;
  		while ((b = readByte()) != -1 && isSpaceChar(b))
  			;
  		return b;
  	}
  
  	private double nd() {
  		return Double.parseDouble(ns());
  	}
  
  	private char nc() {
  		return (char) skip();
  	}
  
  	private String ns() {
  		int b = skip();
  		StringBuilder sb = new StringBuilder();
  		while (!(isSpaceChar(b))) { // when nextLine, (isSpaceChar(b) && b != '
  									// ')
  			sb.appendCodePoint(b);
  			b = readByte();
  		}
  		return sb.toString();
  	}
  
  	private char[] ns(int n) {
  		char[] buf = new char[n];
  		int b = skip(), p = 0;
  		while (p < n) {
  			if (!(isSpaceChar(b)))
  				buf[p++] = (char) b;
  			b = readByte();
  		}
  		return n == p ? buf : Arrays.copyOf(buf, p);
  	}
  
  	private char[][] nm(int n, int m) {
  		char[][] map = new char[n][];
  		for (int i = 0; i < n; i++)
  			map[i] = ns(m);
  		return map;
  	}
  
  	private int[] na(int n) {
  		int[] a = new int[n];
  		for (int i = 0; i < n; i++)
  			a[i] = ni();
  		return a;
  	}
  
  	private List<Integer> na2(int n) {
  		List<Integer> a = new ArrayList<Integer>();
  		for (int i = 0; i < n; i++)
  			a.add(ni());
  		return a;
  	}
  
  	private int[][] na(int n, int m) {
  		int[][] a = new int[n][];
  		for (int i = 0; i < n; i++)
  			a[i] = na(m);
  		return a;
  	}
  
  	private int ni() {
  		int num = 0, b;
  		boolean minus = false;
  		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
  			;
  		if (b == '-') {
  			minus = true;
  			b = readByte();
  		}
  
  		while (true) {
  			if (b >= '0' && b <= '9') {
  				num = num * 10 + (b - '0');
  			} else {
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  
  	private long[] nl(int n) {
  		long[] a = new long[n];
  		for (int i = 0; i < n; i++)
  			a[i] = nl();
  		return a;
  	}
  
  	private long[][] nl(int n, int m) {
  		long[][] a = new long[n][];
  		for (int i = 0; i < n; i++)
  			a[i] = nl(m);
  		return a;
  	}
  
  	private long nl() {
  		long num = 0;
  		int b;
  		boolean minus = false;
  		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
  			;
  		if (b == '-') {
  			minus = true;
  			b = readByte();
  		}
  
  		while (true) {
  			if (b >= '0' && b <= '9') {
  				num = num * 10 + (b - '0');
  			} else {
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  
  	private static void tr(Object... o) {
  		System.out.println(Arrays.deepToString(o));
  	}
  
  }
  