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: #include <bits/stdc++.h>
  using namespace std;
  char gc() {
    static char buf[1 << 16], *s, *t;
    if (s == t) {
      t = (s = buf) + fread(buf, 1, 1 << 16, stdin);
      if (s == t) return EOF;
    }
    return *s++;
  }
  int read() {
    char c;
    int w = 1;
    while ((c = getchar()) > '9' || c < '0')
      if (c == '-') w = -1;
    int ans = c - '0';
    while ((c = getchar()) >= '0' && c <= '9')
      ans = (ans << 1) + (ans << 3) + c - '0';
    return ans * w;
  }
  const int xx = 1e5 + 5;
  int a[xx];
  vector<int> p[558];
  int n;
  int s[558];
  int main() {
    for (int i = 0; i <= 555; i++) s[i] = 1e9;
    s[0] = 0;
    n = read();
    for (int i = 1; i <= n; i++) {
      a[i] = read();
      p[a[i]].push_back(i);
    }
    for (int i = 1; i <= 555; i++) {
      for (int j = 0; j <= 555; j++) {
        if (s[j] != 1e9) {
          vector<int>::iterator it = lower_bound(p[i].begin(), p[i].end(), s[j]);
          if (it != p[i].end()) {
            s[j ^ i] = min(s[j ^ i], *it);
          }
        }
      }
    }
    int ss = 0;
    for (int i = 0; i <= 555; i++) {
      if (s[i] != 1e9) ss++;
    }
    cout << ss << "\n";
    for (int i = 0; i <= 555; i++) {
      if (s[i] != 1e9) cout << i << " ";
    }
    puts("");
    return 0;
  }
  