#include <iostream>
using namespace std;

__int128 vs[62];

int main() {
    cin.tie(nullptr), ios::sync_with_stdio(false);

    int N;
    cin >> N;

    for (int i = 0; i < N; ++i) {
        long long a;
        cin >> a;
        __int128 u = (__int128(a) << 64) + (__int128(1) << i);
        for (int j = 0; j < i; ++j) {
            if (u > (u ^ vs[j])) u ^= vs[j];
        }

        if (u < (__int128(1) << 64)) {

            cout << __builtin_popcountll((long long)u) << "\n";
            for (int d = 0; d < 64; ++d) {
                if ((u >> d) & 1) cout << d + 1 << " ";
            }
            cout << "\n";
            return 0;
        }

        vs[i] = u;
    }

    cout << -1 << "\n";
}