#include <bits/stdc++.h>
#define int long long
#define x first
#define y second
#define pi acos(-1)
using namespace std;
using LL = long long;
using ULL = unsigned long long;
typedef pair<int, int> PII;
const int N = 1e6 + 10, M = 5010, mod = 1e9 + 7;
void solve() {
	int n;
	cin >> n;
	vector <int> a(n + 1);
	int p = 0;
	unordered_map <int, int> mp;
	int p2 = 0, p3 = 0;
	for(int i = 1; i <= n; i++){
		cin >> a[i];
		if(a[i] == 0){
			p = i;
		}
		if(mp[a[i]] != 0){
			p2 = mp[a[i]];
			p3 = i;
		}
		mp[a[i]] = i;
	}
	if(p != 0){
		cout << 1 << "\n";
		cout << p << "\n";
		return;
	}
	if(p2 != 0){
		cout << 2 << "\n";
		cout << p2 << " " << p3 << "\n";
		return;
	}
	vector <PII> d;
	for(int i = 1; i <= n; i++){
		int num = a[i], idx = (1LL << i);
		vector <int> ans;
		for(auto [u, v]: d){
			if((num ^ u) < num){
				num = (num ^ u);
				idx = (idx ^ v);
			}
		}
		if(num == 0){
			for(int j = 0; j <= 60; j++){
				if((idx >> j) & 1) ans.push_back(j + 1);
			}
			cout << ans.size() << "\n";
			for(auto c : ans) cout << c << " ";
			cout << "\n";
			return;
		}
		d.push_back({num, idx});
	}
	cout << -1 << "\n";
	
}
signed main() {
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	int T = 1;
	//cin >> T;
	while(T--) {
		solve();
	}
}