#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <int D>
struct Basis {
  std::vector<std::bitset<D>> v;
  std::vector<int> msb;

  Basis() = default;

  bool add(std::bitset<D> val) {
    const int n = rank();
    if (n == D) return false;
    for (int i = 0; i < n; ++i) {
      if (val[msb[i]]) val ^= v[i];
    }
    if (val.none()) return false;
    int m = D - 1;
    while (!val[m]) --m;
    if (v.empty()) [[unlikely]] {
      v.emplace_back(val);
      msb.emplace_back(m);
      return true;
    }
    const int idx = std::distance(std::upper_bound(msb.rbegin(), msb.rend(), m),
                                  msb.rend());
    v.emplace(std::next(v.begin(), idx), val);
    msb.emplace(std::next(msb.begin(), idx), m);
    for (int i = idx + 1; i <= n; ++i) {
      if (v[idx][msb[i]]) v[idx] ^= v[i];
    }
    for (int i = idx - 1; i >= 0; --i) {
      if (v[i][m]) v[i] ^= v[idx];
    }
    return true;
  }

  int rank() const { return v.size(); }

  inline bool operator<(const Basis& x) const {
    const int n = v.size();
    if (n != x.rank()) return n < x.rank();
    if (n == D) return false;
    for (int i = 0; i < n; ++i) {
      if (msb[i] != x.msb[i]) return msb[i] < x.msb[i];
    }
    for (int i = 0; i < n; ++i) {
      for (int j = msb[i] - 1; ; --j) {
        if (v[i][j] != x.v[i][j]) return x.v[i][j];
      }
    }
    return false;
  }
};

int main() {
  constexpr int B = 60;
  int n; cin >> n;
  vector<int> a;
  a.reserve(n);
  {
    Basis<B> basis;
    bool has_b = false;
    while (n--) {
      int a_i; cin >> a_i;
      const bool is_added = basis.add(a_i);
      a.emplace_back(a_i);
      if (!is_added) {
        has_b = true;
        break;
      }
    }
    if (!has_b) {
      cout << "-1\n";
      return 0;
    }
  }
  n = a.size();
  vector<int> exists(n, true);
  for (int i = n - 2; i >= 0; --i) {
    Basis<B> basis;
    int rank = 0;
    REP(j, n) {
      if (j != i && exists[j]) {
        basis.add(a[j]);
        ++rank;
      }
    }
    if (basis.rank() < rank) exists[i] = false;
  }
  vector<int> b;
  REP(i, n) {
    if (exists[i]) b.emplace_back(i);
  }
  const int m = b.size();
  cout << m << '\n';
  REP(i, m) cout << b[i] + 1 << " \n"[i + 1 == m];
  return 0;
}