#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
 
    ll N, A;
    cin >> N;
    vector<pair<ll, ll>> vec(N);
    vector<pair<ll, ll>> base;
    
    for (int i=0; i<N; i++){
        cin >> A;
        vec[i] = {A, (i<=60 ? (1LL<<i) : -1)};
    }
    
    for (int i=0; i<N; i++){
        for (auto [e, x] : base){
            if ((vec[i].first^e) < vec[i].first){
                vec[i].first ^= e;
                vec[i].second ^= x;
            }
        }
        if (vec[i].first) base.push_back(vec[i]);
        else{
            vector<ll> ans;
            for (int j=0; j<=60; j++){
                if (vec[i].second & (1LL<<j)){
                    ans.push_back(j+1);
                }
            }
            cout << ans.size() << endl;
            for (auto x : ans) cout << x << " ";
            cout << endl;
            return 0;
        }
    }

    cout << -1 << endl;

    return 0;
}