#include <bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T> istream& operator >> (istream& is, vector<T>& vec) {
    for(T& x : vec) is >> x;
    return is;
}

template<class T> ostream& operator << (ostream& os, const vector<T>& vec) {
    if(vec.empty()) return os;
    os << vec[0];
    for(auto it = vec.begin(); ++it != vec.end(); ) os << ' ' << *it;
    return os;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<ll> a(n), b, idx, U;
    cin >> a;
    for(int i = 0; i < n; i++){
        int S = 0;
        for(int j = 0; j < b.size(); j++){
            ll v = a[i] ^ b[j];
            if (v < a[i]){
                a[i] = v;
                S ^= U[j];
            }
        }
        if(a[i] == 0){
            vector<int> ans = {i + 1};
            for(int j = 0; j < b.size(); j++){
                if(S >> j & 1) ans.emplace_back(idx[j] + 1);
            }
            cout << ans.size() << '\n';
            cout << ans << '\n';
            return 0;
        }else{
            U.emplace_back(S | (1 << b.size()));
            b.emplace_back(a[i]);
            idx.emplace_back(i);
        }
    }
    cout << -1 << '\n';
}