#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];
    n = min(n, 61);
    
    vector<vector<bool>> used(n, vector<bool>(n, false));
    vector<pair<ll, int>> B;
    for(int i=0; i<n; i++){
        ll now = A[i];
        used[i][i] = true;
        for(auto [b, j] : B){
            if((now^b) < now){
                used[i][j] = true;
                now = now^b;
            }
        }

        if(now==0){
            vector<vector<bool>> cnt(i+1, vector<bool>(i+1, false));
            for(int j=0; j<=i; j++){
                for(int k=0; k<j; k++) if(used[j][k]){
                    for(int l=0; l<n; l++) cnt[j][l] = cnt[j][l] ^ cnt[k][l];
                }
                cnt[j][j] = true;
            }

            vector<int> ans;
            for(int j=0; j<=i; j++) if(cnt[i][j]) ans.pb(j);
            cout << (int)ans.size() << '\n';
            for(int j : ans) cout << j+1 << ' ';
            cout << '\n';
            return;
        }else{
            used[i][i] = true;
            B.pb({now, i});
        }
    }

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

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