#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define ALL(v) v.begin(),v.end()
#define dbg(x) cerr << #x << ": " << (x) << endl;
int n;
vector<ll> a;
int main() {
    cin >> n;
    a.resize(n);
    for (int i = 0; i < n; ++i) cin >> a[i];

    vector<pair<ll,ll>> bases;
    for (int i = 0; i < n; ++i) {
        ll y = a[i];
        ll mask = 1LL << i;
        for (auto [b,index] : bases) {
            if ((b ^ y) < y) {
                y ^= b;
                mask ^= index;
            }
        }
        if (y) {
            bases.emplace_back(y, mask);
        }
        else {
            vector<int> v;
            for (int j = 0; j <= 60; ++j) if (mask >> j & 1) {
                v.push_back(j);
            }
            cout << v.size() << '\n';
            for (int j = 0; j < v.size(); ++j) {
                cout << v[j]+1 << " \n"[j==v.size()-1];
            }
            return 0;
        }
    }
    cout << -1 << '\n';
}