#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, t) for (ll i = s; i < (ll)(t); i++)

template<typename T>
bool chmin(T &x, T y) { return x > y ? (x = y, true) : false; }
template<typename T>
bool chmax(T &x, T y) { return x < y ? (x = y, true) : false; }

struct io_setup {
	io_setup() {
		ios::sync_with_stdio(false);
		std::cin.tie(nullptr);
		cout << fixed << setprecision(15);
	}
} io_setup;

int main(){
	int n;
	cin>>n;
	vector<int> a(n);
	rep(i,0,n) cin>>a.at(i);
	vector<int> b;
	vector<pair<int,vector<int>>> ck;
	rep(i,0,n){
		int x=a.at(i);
		vector<int> v;
		int ct=0;
		for(int y:b){
			if(chmin(x,x^y)) v.push_back(ct);
			ct++;
		}
		if(x==0){
			vector<int> ans;
			ans.push_back(i);
			int m=b.size();
			vector<int> us(m,0);
			for(int d:v) us.at(d)^=1;
			while(!us.empty()){
				if(us.back()){
					auto[dd,tv]=ck.back();
					ans.push_back(dd);
					for(int d:tv) us.at(d)^=1;
				}
				us.pop_back();				
				ck.pop_back();
			}
			m=ans.size();
			cout<<m<<"\n";
			rep(j,0,m) cout<<ans.at(j)+1<<" \n"[j==m-1];
			return 0;
		}
		b.push_back(x);
		ck.push_back({i,v});
	}
	cout<<"-1\n";
}