#include <bits/stdc++.h>
using namespace std;
using namespace std;
template <typename T, typename U>
std::istream& operator>>(std::istream& i, pair<T, U>& p) {
  i >> p.first >> p.second;
  return i;
}
template <typename T>
std::istream& operator>>(std::istream& i, vector<T>& t) {
  for (auto& v : t) {
    i >> v;
  }
  return i;
}
template <typename T, typename U>
std::ostream& operator<<(std::ostream& o, const pair<T, U>& p) {
  o << p.first << ' ' << p.second;
  return o;
}
template <typename T>
std::ostream& operator<<(std::ostream& o, const vector<T>& t) {
  if (t.empty()) o << '\n';
  for (size_t i = 0; i < t.size(); ++i) {
    o << t[i] << " \n"[i == t.size() - 1];
  }
  return o;
}
template <typename T>
using minheap = priority_queue<T, vector<T>, greater<T>>;
template <typename T>
using maxheap = priority_queue<T, vector<T>, less<T>>;
template <typename T>
bool in(T a, T b, T c) {
  return a <= b && b < c;
}
unsigned int logceil(int x) { return 8 * sizeof(int) - __builtin_clz(x); }
namespace std {
template <typename T, typename U>
struct hash<pair<T, U>> {
  hash<T> t;
  hash<U> u;
  size_t operator()(const pair<T, U>& p) const {
    return t(p.x) ^ (u(p.y) << 7);
  }
};
}  // namespace std
template <typename T>
T gcd(T a, T b) {
  if (a < b) swap(a, b);
  return b ? gcd(b, a % b) : a;
}
template <typename T>
class vector2 : public vector<vector<T>> {
 public:
  vector2() {}
  vector2(size_t a, size_t b, T t = T())
      : vector<vector<T>>(a, vector<T>(b, t)) {}
};
template <typename T>
class vector3 : public vector<vector2<T>> {
 public:
  vector3() {}
  vector3(size_t a, size_t b, size_t c, T t = T())
      : vector<vector2<T>>(a, vector2<T>(b, c, t)) {}
};
template <typename T>
class vector4 : public vector<vector3<T>> {
 public:
  vector4() {}
  vector4(size_t a, size_t b, size_t c, size_t d, T t = T())
      : vector<vector3<T>>(a, vector3<T>(b, c, d, t)) {}
};
template <typename T>
class vector5 : public vector<vector4<T>> {
 public:
  vector5() {}
  vector5(size_t a, size_t b, size_t c, size_t d, size_t e, T t = T())
      : vector<vector4<T>>(a, vector4<T>(b, c, d, e, t)) {}
};
void fastIO() { ios::sync_with_stdio(false); }
template <typename T, typename... Args>
T max(T t, Args... args) {
  return max(max<T>(args...), t);
}
template <typename T, typename... Args>
T min(T t, Args... args) {
  return min(min<T>(args...), t);
}
int b[32];
int sz = 0;
bool add(int x) {
  for (int i = 0; i < sz; i++)
    if ((x ^ b[i]) < x) x ^= b[i];
  for (int i = 0; i < sz; i++)
    if ((x ^ b[i]) < b[i]) b[i] ^= x;
  if (x) {
    b[sz++] = x;
    for (int i = sz - 1; i; i--)
      if (b[i] < b[i - 1]) swap(b[i], b[i - 1]);
    return true;
  }
  return false;
}
vector<int> getBas(vector<int>& v, int k) {
  sz = 0;
  int mx = 1 << k;
  vector<int> ans;
  for (auto e : v) {
    if (e >= mx) continue;
    if (add(e)) ans.push_back(e);
  }
  return ans;
}
class EVolshebniePerestanovki {
 public:
  void solve(std::istream& in, std::ostream& out) {
    int n;
    in >> n;
    vector<int> v(n);
    in >> v;
    for (int i = 20 - 1; i >= 0; --i) {
      vector<int> bas = getBas(v, i);
      if (bas.size() == i) {
        out << i << endl;
        for (int j = 0; j < 1 << i; ++j) {
          int num = j ^ (j >> 1);
          int val = 0;
          for (int u = 0; u < i; ++u) {
            if (num & (1 << u)) val ^= bas[u];
          }
          out << val << " ";
        }
        return;
      }
    }
  }
};
int main() {
  EVolshebniePerestanovki solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}
