Split string into equal chunks, C#

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//Title of this code
//Rextester.Program.Main is the entry point for your code. Don't change it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Split("123", 2).ForEach(f => Console.WriteLine(f));
        }
        
        public static List<string> Split(string str, int chunks)
        {
            var l = new List<string>();
            if (string.IsNullOrEmpty(str))
                return l;
            if (str.Length < chunks)
            {
                l.Add(str);
                return l;
            }
            int chunkSize = str.Length / chunks;

int stringLength = str.Length;
            for (int i = 0; i < stringLength; i += chunkSize)
            {
                if (i + chunkSize > stringLength)
                    chunkSize = stringLength - i;
                l.Add(str.Substring(i, chunkSize));
            }
            string residual = "";
            l.Where((f, i) => i > chunks - 1).ToList().ForEach(f => residual += f);
            l[chunks - 1] += residual;
            return l.Take(chunks).ToList();
        }
    }
}

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Compilation time: 0.14 sec, absolute running time: 0.09 sec, cpu time: 0.08 sec, average memory usage: 16 Mb, average nr of threads: 4