using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var a = NList;
        for (var i = 0; i < n; ++i) if (a[i] == 0)
        {
            WriteLine(1);
            WriteLine(i + 1);
            return;
        }
        var bitmax = 60;
        if (a.Length > bitmax + 1)
        {
            n = bitmax + 1;
            a = a.Take(n).ToArray();
        }
        var map = new int[bitmax][];
        for (var i = 0; i < bitmax; ++i)
        {
            map[i] = new int[n + 1];
            for (var j = 0; j < n; ++j) map[i][j] = (int)((a[j] >> i) & 1);
        }
        GaussJordanEliminationXor(map);
        var ans = Check(map);
        if (ans.Length == 0) WriteLine(-1);
        else
        {
            var a2 = new List<int>();
            for (var i = 0; i < ans.Length; ++i) if (ans[i] != 0) a2.Add(i + 1);
            WriteLine(a2.Count);
            WriteLine(string.Join(" ", a2));
        }
    }
    // XOR(= mod2の足し算)で掃き出し法を行う
    static void GaussJordanEliminationXor(int[][] map)
    {
        // 標準系にする
        var px = -1;
        for (var j = 0; j < map[0].Length - 1; ++j)
        {
            var x = px + 1;
            if (x >= map.Length) break;
            var sw = -1;
            for (var i = x; i < map.Length; ++i) if (map[i][j] != 0)
            {
                sw = i;
                break;
            }
            if (sw < 0) continue;
            if (x != sw) (map[x], map[sw]) = (map[sw], map[x]);
            for (var i = 0; i < map.Length; ++i) if (i != x)
            {
                if (map[i][j] != 0)
                {
                    for (var p = j; p < map[i].Length; ++p) map[i][p] = (map[i][p] + map[x][p]) & 1;
                }
            }
            px = x;
        }
    }
    // 掃き出し法の結果から解を求める
    static int[] Check(int[][] map)
    {
        var n = map[0].Length - 1;
        var iskey = new bool[n];
        var isfree = new bool[n];
        for (var i = 0; i < map.Length; ++i)
        {
            var flg = true;
            for (var j = 0; j < n; ++j) if (map[i][j] != 0)
            {
                if (flg)
                {
                    iskey[j] = true;
                }
                else
                {
                    isfree[j] = true;
                }
                flg = false;
            }
            // 解なしチェック
            if (flg && map[i][^1] != 0) return new int[0];
        }
        var ans = new int[n];
        // (この問題のみ)
        // freeがない場合解なし
        // freeのうち最初のみ1に設定し、あとは0に設定
        if (isfree.All(f => !f)) return new int[0];
        for (var i = 0; i < n; ++i) if (isfree[i])
        {
            ans[i] = 1;
            break;
        }
        for (var i = 0; i < map.Length; ++i)
        {
            var pos = -1;
            for (var j = 0; j < n; ++j) if (map[i][j] != 0)
            {
                if (pos < 0) pos = j;
                else
                {
                    ans[pos] = (ans[pos] + ans[j]) % 2;
                }
            }
            if (pos >= 0) ans[pos] = (ans[pos] + map[i][^1]) % 2;
        }
        return ans;
    }
}