#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10, lg = 20;
int n, s[N], lb[lg + 5], id[lg + 5];
int a[1 << (lg + 1)], tot = 0;
void inser(int x, int p) {
  for (int i = lg; i >= 0; i--) {
    if (!((x >> i) & 1)) continue;
    if (!lb[i])
      return lb[i] = x, id[i] = p, void();
    else
      x ^= lb[i];
  }
  return;
}
int check(int x) {
  for (int i = 0; i <= lg; i++) id[i] = lb[i] = 0;
  for (int i = 1; i <= n; i++) {
    if (s[i] >= (1 << x)) continue;
    inser(s[i], i);
  }
  for (int i = x - 1; i >= 0; i--)
    if (lb[i] == 0) return 0;
  return 1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &s[i]);
  }
  int x = 0;
  for (int i = lg + 1; i >= 0; i--) {
    if (check(i)) {
      x = i;
      break;
    }
  }
  a[0] = 0, tot = 1;
  for (int i = 0; i <= x - 1; i++) {
    int v = s[id[i]];
    for (int j = 0; j < tot; j++) {
      a[tot * 2 - 1 - j] = a[j] ^ v;
    }
    tot *= 2;
  }
  printf("%d\n", x);
  for (int i = 0; i < tot; i++) printf("%d ", a[i]);
  printf("\n");
  return 0;
}
