#include <bits/stdc++.h>

using ll = std::int64_t;

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

    int N;
    std::cin >> N;

    std::vector<ll> basis, coef, pos;
    for(int i=0;i<N;i++){
        ll A;
        std::cin >> A;

        ll c = 0;
        for(int j=0;j<basis.size();j++){
            if((A ^ basis[j]) < A){
                A ^= basis[j];
                c ^= coef[j];
            }
        }

        if(A > 0){
            c |= 1ll << basis.size();

            basis.emplace_back(A);
            coef.emplace_back(c);
            pos.emplace_back(i + 1);
        }else{
            std::vector<ll> B;
            for(int j=0;j<basis.size();j++){
                if(c >> j & 1){
                    B.emplace_back(pos[j]);
                }
            }
            B.emplace_back(i + 1);

            std::cout << B.size() << std::endl;
            for(int j=0;j<B.size();j++){
                std::cout << B[j] << " \n"[j + 1 == B.size()];
            }

            return 0;
        }
    }

    std::cout << -1 << std::endl;
}