#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	/*int n; cin >> n;
	vector<long long>a(n);
	rep(i, n)cin >> a[i];
	std::vector<pair<long long, long long>>base;
	for (int i = 0; i < (int)a.size(); ++i) {
		auto value = a[i];
		long long index = 1ll << i;
		for (int j = 0; j < base.size(); ++j) {
			if (value ^ base[j].first < value) {
				value ^= base[j].first;
				index ^= base[j].second;
			}
		}
		if (value == 0) {
			vector<int>ans;
			rep(j, 60) {
				if (1 & (index >> j)) {
					ans.push_back(j);
				}
			}
			cout << ans.size() << endl;
			for (int e : ans) cout << e + 1 << " ";
			cout << endl;
			return 0;
		}
		base.emplace_back(value, index);
	}
	cout << -1 << endl;*/

	int n; cin >> n;
	vector<long long> a(n);
	rep(i, n)cin >> a[i];
	vector<pair<long long, long long>> base;
	for (int i = 0; i < a.size(); i++) {
		long long value = a[i];
		long long index = 1ll << i; 
		for (int j = 0; j < base.size(); ++j) {
			if ((value ^ base[j].first) < value) {
				value ^= base[j].first;
				index ^= base[j].second;
			}
		}
		if (value == 0) {
			vector<int> ans;
			rep(j, 61) {
				if (1 & (index >> j)) {
					ans.push_back(j);
				}
			}
			cout << ans.size() << endl;
			for (int e : ans) cout << e + 1 << " ";
			cout << endl;
			return 0;
		}
		base.emplace_back(value, index);
	}

	cout << -1 << endl;
	return 0;
}