typedef long long ll;
typedef long double ld;

#include <bits/stdc++.h>
using namespace std;

signed main(){
    ll n;
    std::cin >> n;
    vector<ll> a(n);
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
    }
    set<ll> s;
    map<ll,ll> vals;
    map<ll,ll> inds;
    n = min(60ll,n);
    for (int i = 0; i < n; i++) {
        ll index = (1ll<<i);
        ll val = a[i];
        for (auto e : s) {
            if(val>(vals[e]^val)){
                val ^= vals[e];
                index ^= inds[e];
            }
        }
        // std::cout << index<<" "<<val << std::endl;
        if(val!=0){
            s.insert(i);
            vals[i] = val;
            inds[i] = index;
        }else{
            vector<ll> ans;
            for (int i = 0; i < n; i++) {
                if(index&(1ll<<i)){
                    ans.push_back(i);
                }
            }
            std::cout << ans.size() << std::endl;
            for (auto e : ans) {
                std::cout << e+1<<" ";
            }
            std::cout << std::endl;
            return 0;
        }
        
    }
    std::cout << -1 << std::endl;
};