#include<bits/stdc++.h>
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];
    }
    sort(A.begin(),A.end());
    vector<ll> B;
    for(int i=0;i<N;i++){
        vector<int> ID;
        for(int j=0;j< B.size();j++) {
            if ((A[i] ^ A[B[j]]) < A[i]) {
                A[i] ^= A[B[j]];
                ID.push_back(B[j]);
            }
        }
        for (auto&& b : B) {
            if ((A[i] ^ A[b]) < A[b])A[b] ^= A[i];
        }
        if (A[i] > 0) {
            B.push_back(i);
        }
        else{
            ID.push_back(i);
            int an=ID.size();
            cout<<an<<endl;;
            for(int j=0;j<an;j++)cout<<ID[j]+1<<" \n"[j==an-1];
            return 0;
        }
    }
    cout<<-1<<endl;
}