#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n;
    cin >> n;
    vector<ll> a(n);
    rep(i,n) cin >> a[i];
    vector<P> base;
    rep(i,n) {
        ll now = a[i];
        ll idx = 1ll<<i;
        for(auto [val, id] : base) {
            if(now > (now^val)) {
                now ^= val;
                idx ^= id;
            }
        }
        if(now==0) {
            vector<int> ans;
            rep(j,i+1) {
                if(idx>>j&1) ans.push_back(j+1);
            }
            cout << ans.size() << endl;
            for(int a : ans) {
                cout << a << " ";
            }
            cout << endl;
            return 0;
        }
        base.emplace_back(now, idx);
    }
    cout << -1 << endl;
    return 0;
}