#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
const ll MOD1000000007 = 1000000007;
const ll MOD998244353 = 998244353;
const ll MOD[3] = {999727999, 1070777777, 1000000007};
const ll LINF = 1LL << 60LL;
const int IINF = (1 << 30) - 2;


void solve(){
    int n; cin >> n;
    vector<ll> a(n);
    for(int i=0; i<n; i++) cin >> a[i];
    
    vector<int> B;
    for(int i=0; i<n; i++){
        vector<int> ans;
        ll e = a[i];
        for(int j : B){
            if((e^a[j]) < e){
                ans.pb(j);
                e ^= a[j];
            }
        }
        if(e==0){
            ans.pb(i);
            cout << (int)ans.size() << '\n';
            for(int idx : ans) cout << idx+1 << ' ';
            cout << '\n';
            return;
        }else{
            B.pb(i);
        }
    }

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

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int T=1;
    //cin >> T;
    while(T--) solve();
}