#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int n;
  cin >> n;
  vector<long long> a(n);
  for (int i = 0; i < n; ++i) cin >> a[i];
  vector<pair<long long, int>> bs;
  vector<vector<int>> val;
  for (int i = 0; i < n; ++i)
  {
    long long tmp = a[i];
    int siz = bs.size();
    vector<int> ids;
    for (int j = 0; j < siz; ++j)
    {
      if (tmp > (tmp ^ bs[j].first))
      {
        tmp ^= bs[j].first;
        ids.push_back(j);
      }
    }
    if (tmp == 0)
    {
      vector<int> cnt(n);
      cnt[i] = 1;
      for (int v : ids)
      {
        for (auto id : val[v])
        {
          cnt[id] ^= 1;
        }
      }
      vector<int> ans;
      for (int j = 0; j < n; ++j) if (cnt[j]) ans.push_back(j + 1);
      cout << ans.size() << endl;
      for (auto v : ans) cout << v << ' ';
      cout << endl;
      return 0;
    }
    else
    {
      vector<int> cnt(n);
      cnt[i] = 1;
      for (auto v : ids)
      {
        for (auto id : val[v])
        {
          cnt[id] ^= 1;
        }
      }
      vector<int> tmpid;
      for (int j = 0; j < n; ++j)
      {
        if (cnt[j])
        {
          tmpid.push_back(j);
        }
      }
      val.push_back(tmpid);
      bs.emplace_back(tmp, i);
    }
  }
  cout << -1 << endl;
}