#ifdef ONLINE_JUDGE
#pragma GCC optimize(3, "Ofast", "inline")
#endif
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define rt return
#define pi pair<int, int>
#define pl pair<ll, ll>
#define pu pair<ull, ull>
#define int long long
#define ll long long
#define ull unsigned long long
#define endl '\n'
#define Endl endl
#define all(x) x.begin(), x.end()
#define all1(x) next(x.begin()), x.end()
#define lll __int128_t
#define ulll __uint128_t
using namespace std;
const int maxn = 1e5 + 50;
const int mod = 998244353;
const ll maxl = 2e18 + 5;
const int maxi = 1e9 + 7;
struct LinearBase
{
    // ????? idx?1??
    // ????? idx?0??
    int N;
    vector<ull> base;
    vector<int> idx;
    int iffzero = 0;
    LinearBase()
    {
        N = 105;
        base.resize(102);
    }
    LinearBase(int n)
    {
        N = n + 5;
        base.resize(n + 20);
        idx.resize(n + 20);
    }
    void clear()
    {
        N = 0;
        base.clear();
    }
    bool insert(ull x, int dx)
    {
        assert(N != 0);
        for (int i = 62; i >= 0; i--)
        {
            if (!(x & (1ull << i)))
                continue;
            if (!base[i])
            {
                base[i] = x;
                idx[i] = dx;
                return 1;
            }
            x ^= base[i];
            if (x == 0)
            {
                iffzero = 1;
                return false;
            }
        }
        return 1;
    }
    void goass()
    {
        assert(N != 0);
        sort(base.begin(), base.end(), greater<ull>());
        int row = 0;
        for (int i = 62; i >= 0; i--)
        {
            for (int j = row; j < N; j++)
            {
                if ((1ull << i) & base[j])
                {
                    swap(base[j], base[row]);
                }
            }
            if (!((1ull << i) & base[row]))
                continue;
            for (int j = 0; j < N; j++)
            {
                if (j == row)
                    continue;
                if ((1ull << i) & base[j])
                {
                    base[j] ^= base[row];
                }
            }
            row++;
        }
    }
    void printbi(ull x)
    {
        for (int j = 62; j >= 0; j--)
        {
            if ((1ull << j) & x)
            {
                cerr << 1;
            }
            else
                cerr << 0;
        }
        cerr << endl;
    }
    void print()
    {
        assert(N != 0);
        for (int i = 0; i < N; i++)
        {
            for (int j = 62; j >= 0; j--)
            {
                if ((1ull << j) & base[i])
                {
                    cerr << 1;
                }
                else
                    cerr << 0;
            }
            cerr << endl;
        }
        cerr << endl;
    }
};
void init()
{
}
void solve()
{
    int n;
    cin >> n;
    vector<int> a(n + 1);
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    LinearBase lb(105);
    vector<int> ans;
    for (int i = 1; i <= n; i++)
    {
        if (!lb.insert(a[i], i))
        {
            ull x = a[i];
            for (int j = 62; j >= 0; j--)
            {
                if (!(x & (1ull << j)))
                    continue;
                x ^= lb.base[j];
                if(lb.idx[j]!=0)
                ans.push_back(lb.idx[j]);
            }
            ans.push_back(i);
            break;
        }
    }
    if(ans.empty())
    {
        cout<<-1<<endl;
    }
    else
    {
        cout<<ans.size()<<endl;
        for(int i=0;i<ans.size();i++)
        {
            cout<<ans[i]<<" \n"[i==ans.size()-1];
        }
    }
}
signed main()
{
#ifndef ONLINE_JUDGE
    freopen("1.txt", "r", stdin);
    freopen("2.txt", "w", stdout);
#endif
    std::ios::sync_with_stdio(0);
    std::cin.tie(0);
    int __ = 1;
    // std::cin >> __;
    init();
    while (__--)
    {
        solve();
        // cerr<<"TIME"<<qq-__<<endl;
    }
    return 0;
}