#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
using ll = long long;


int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n;
    cin>>n;
    vector<ll> a(n);
    for(int i = 0;i<n;i++){
        cin>>a[i];
    }
    vector<ll> now,use;
    for(int i = 0;i<n;i++){
        ll all = 0;
        ll aa = a[i];
        all |= 1ll << i;
        for(int i = 0;i<now.size();i++){
            ll e = now[i];
            ll nxt = e ^ aa;
            if(nxt<aa){
                aa = nxt;
                all ^= use[i];
            }
        }
        if(aa!=0){
            now.push_back(aa);
            use.push_back(all);
            continue;
        }
        vector<int> ans;
        for(int j = 0;j<63;j++){
            if(all>>j&1) ans.push_back(j+1);
        }
        cout<<ans.size()<<endl;
        for(int j = 0;j<ans.size();j++){
            if(j) cout<<" ";
            cout<<ans[j];
        }
        cout<<endl;
        return 0;
    }
    cout<<-1<<endl;
}