#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};
    ll B[200009]={0};

    ll i,j,k;

    cin>>N;
    rep(i,N)cin>>A[i];
    rep(i,N)B[i]=A[i];

    bool pivot[200009]={0};
    vector<ll> use(60,-1);

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

    bool ans=0;
    rep(i,N){
        if(A[i]==0){
            vector<ll>list;
            list.push_back(i);
            for(k=59;0<=k;k--){
                if(use[k]==-1)continue;
                if(B[i]<=(B[i]^B[use[k]]))continue;
                B[i]^=B[use[k]];
                list.push_back(use[k]);
            }
            if(B[i]!=0)continue;
            ans=1;
            sort(list.begin(),list.end());
            cout<<list.size()<<endl;
            rep(j,list.size())cout<<list[j]+1<<' ';
            cout<<endl;
            break;
        }
    }
    if(ans==0)cout<<-1<<endl;

    return 0;
}