#include<bits/stdc++.h>
using namespace std;
#define rep(i,N) for(i=0;i<N;i++)
#define ll long long

int main(void){
    ll N;
    ll A[200009]={0};
    vector<ll>use[200009];

    ll i,j,k;

    cin>>N;
    rep(i,N)cin>>A[i];
    rep(i,N)use[i].push_back(i);

    set<ll>pivot;

    for(k=59;0<=k;k--){
        rep(j,N){
            if(pivot.find(j)!=pivot.end())continue;
            if((A[j]&(1LL<<k))!=0)break;
        }
        if(j==N)continue;
        pivot.insert(j);
        rep(i,N){
            if(i==j)continue;
            if((A[i]&(1LL<<k))==0)continue;
            A[i]^=A[j];
            use[i].push_back(j);
        }
    }

    bool ans=0;
    rep(i,N){
        if(A[i]==0){
            ans=1;
            cout<<use[i].size()<<endl;
            for(auto e:use[i]){
                cout<<e+1<<' ';
            }
            cout<<endl;
            break;
        }
    }
    if(ans==0)cout<<-1<<endl;

    return 0;
}