#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<vector<ll>> b(n);
  rep(i, n) {
    ll x;
    cin >> x;
    a[i] = x;
    b[i].push_back(i);
  }
  vector<ll> indeg(n, 0), outdeg(n, 0);
  rep(j, 60) {
    ll k = -1;
    rep(i, n) {
      if (indeg[i] == 0 && outdeg[i] == 0 && a[i].test(j)) {
        k = i;
        outdeg[k] = 1;
        break;
      }
    }
    if (k == -1)
      continue;
    rep(i, n) {
      if (outdeg[i] == 0 && a[i].test(j)) {
        indeg[i] += 1;
        a[i] ^= a[k];
        for (const auto x : b[k]) {
          b[i].push_back(x);
        }
      }
    }
  }
  rep(k, n) if (a[k].count() == 0) {
    sort(b[k].begin(), b[k].end());
    cout << b[k].size() << '\n';
    rep(i, b[k].size()) cout << (i ? " " : "") << b[k][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;
}