#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

int main() {
    int N;
    cin >> N;
    vector<pair<ll, int>> A(N);
    for (int i = 0; i < N; i++) {
        cin >> A[i].first;
        A[i].second = i;
    }
    ranges::sort(A);

    for (int i = 0; i < N; i++) {
        if (A[i].first == 0) {
            cout << 1 << endl;
            cout << A[i].second + 1 << endl;
            return 0;
        }
    }

    for (int i = 0; i < N - 1; i++) {
        if (A[i].first == A[i + 1].first) {
            cout << 2 << endl;
            cout << A[i].second + 1 << " " << A[i + 1].second + 1 << endl;
            return 0;
        }
    }

    map<ll, vector<int>> mp;
    mp[0].push_back({-1});
    for (int i = 0; i < N; i++) {
        if (mp.count(A[i].first)) {
            cout << mp[A[i].first].size() << endl;
            for (int j : mp[A[i].first]) {
                if (j == -1) continue;
                cout << j + 1 << " ";
            }
            cout << A[i].second + 1 << endl;
            return 0;
        }
        for (auto p : mp) {
            mp[p.first ^ A[i].first] = p.second;
            mp[p.first ^ A[i].first].push_back(A[i].second);
        }
    }

    cout << -1 << endl;
}