#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main () {
	int N;
	cin >> N;
	vector<pair<ll, ll>> bs;
	for (int i = 0; i < N; i ++) {
		ll a;
		cin >> a;
		ll st = (1ll << i);

		for (auto& [b, s] : bs) {
			if ((a ^ b) < a) {
				a ^= b;
				st ^= s;
			}
		}
		if (a) {
			bs.emplace_back(a, st);
		} else {
			vector<int> ans;
			for (int j = 0; j <= i; j ++) {
				if ((st >> j) & 1) {
					ans.push_back(j+1);
				}
			}
			cout << ans.size() << endl;
			for (auto& p : ans) {
				cout << p << (p == ans.back() ? "" : " ");
			}
			cout << endl;
			return 0;
		}
	}
	puts("-1");
}