#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll n;
  cin >> n;
  vector<bitset<60>> a(n);
  vector<set<ll>> b(n);
  {
    vector<pair<ll, ll>> x(n);
    rep(i, n) cin >> x[i].first, x[i].second = i;
    sort(x.begin(), x.end());
    rep(i, n) a[i] = x[i].first, b[i].insert(x[i].second);
  }
  for (ll j = 59; j >= 0; j--) {
    ll k = -1;
    rep(i, n) {
      if (a[i].test(j)) {
        k = i;
        break;
      }
    }
    if (k == -1)
      continue;
    rep(i, n) if (i != k && a[i].test(j)) {
      a[i] ^= a[k];
      for (const auto x : b[k]) {
        if (b[i].count(x)) {
          b[i].erase(x);
        } else {
          b[i].insert(x);
        }
      }
    }
  }
  rep(k, n) if (a[k].count() == 0) {
    vector<ll> ans(b[k].begin(), b[k].end());
    cout << ans.size() << '\n';
    rep(i, ans.size()) cout << (i ? " " : "") << ans[i] + 1;
    cout << '\n';
    return;
  }
  cout << "-1\n";
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}