#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const int BITLEN=60;

//bitsetの昇順
bool bitasc(const bitset<BITLEN> &a, const bitset<BITLEN> &b){
    for (int i=BITLEN-1; i>=0; i--){
        if (a[i] != b[i]){
            return a[i] < b[i];
        }
    }
    return false;
}

//bitsetのmin
bitset<BITLEN> min(bitset<BITLEN> a, bitset<BITLEN> b){
    if (bitasc(a, b)) return a;
    return b;
}

const ll modc=998244353;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
 
    ll N, A;
    cin >> N;
    vector<pair<bitset<BITLEN>, int>> vec(N);
    vector<pair<bitset<BITLEN>, int>> base;
    
    for (int i=0; i<N; i++){
        cin >> A;
        vec[i] = {A, i};
    }
    //A_iに作用したindex
    vector<vector<ll>> v(N);
    vector<ll> cnt(N), ans;

    auto dfs=[&](auto self, int from)->void{
        cnt[from]++;
        for (auto to : v[from]){
            self(self, to);
        }
    };

    for (int i=0; i<N; i++){
        for (auto &[e, x] : base){
            if (bitasc(vec[i].first^e, vec[i].first)){
                vec[i].first = vec[i].first^e;
                v[i].push_back(x);
            }
        }
        if (vec[i].first.any()) base.push_back(vec[i]);
        else{
            dfs(dfs, i);
            for (int j=0; j<N; j++){
                if (cnt[j] % 2 == 1) ans.push_back(j+1);
            }
            cout << ans.size() << endl;
            for (auto x : ans) cout << x << " ";
            cout << endl;
            return 0;
        }
    }

    cout << -1 << endl;

    return 0;
}