#include<bits/stdc++.h>
// #include<atcoder/all>
// #include<boost/multiprecision/cpp_int.hpp>

using namespace std;
// using namespace atcoder;
// using bint = boost::multiprecision::cpp_int;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<ll,ll>;
using vi = vector<ll>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using ve = vector<vector<int>>;
using vb = vector<bool>;
using vvb = vector<vb>;
#define rep(i,n) for(ll i = 0;i < (ll)n;i++)
#define ALL(x) (x).begin(),(x).end()
#define sz(c) ((ll)(c).size())
#define LB(A,x) (int)(lower_bound(A.begin(),A.end(),x)-A.begin())
#define UB(A,x) (int)(upper_bound(A.begin(),A.end(),x)-A.begin())
// #define MOD 1000000007
#define MOD 998244353
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
template<typename T>ostream&operator<<(ostream&os,vector<T>&v){for(int i = 0;i < v.size();i++)os<<v[i]<<(i+1!=v.size()?" ":"");return os;}
template<typename T>istream&operator>>(istream&is,vector<T>&v){for(T&in:v)is>>in;return is;}
template<typename T1,typename T2>ostream&operator<<(ostream&os,pair<T1,T2>&p){os<<p.first<<" "<<p.second;return os;}
template<typename T1,typename T2>istream&operator>>(istream&is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T> inline bool chmax(T &a,T b){if(a < b){a = b;return true;}return false;}
template<typename T> inline bool chmin(T &a,T b){if(a > b){a = b;return true;}return false;}
ld dist(ld x1,ld y1,ld x2, ld y2){return sqrtl((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}


int main(){
  
  ios_base::sync_with_stdio(0), cin.tie(0);
  int n;cin >> n;
  vi a(n);cin >> a;
  vi base;
  vvi idx;
  rep(i,n){
    int e = a[i];
    vi k;
    rep(j,sz(base)){
      int b = base[j];
      if(chmin(e,e^b)){
        for(auto au : idx[j])k.emplace_back(au);
      }
    }
    k.emplace_back(i);
    if(e){
      base.emplace_back(e);
      idx.emplace_back(k);
    }else{
      vb res(n);
      for(auto au : k){
        res[au] = !res[au];
      }
      vi ans;
      rep(i,n)if(res[i])ans.emplace_back(i+1);
      cout << sz(ans) << "\n";
      cout << ans << "\n";
      return 0;
    }
  }
  cout << "-1\n";
  

  return 0;
}