using System;

using System.Threading.Tasks;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public void Main(){

        foreach(var p in getLine().Select(s => s).GroupAt(3))

        Console.WriteLine(p.Aggregate("",(s,val) => s += val));

    }

    public string getLine(){ return "Hello World, how are you doing, this just some text to show how the grouping works"; }

}

​

public static class GroupExtension

{

    public static IEnumerable<IGrouping<int, T>> GroupAt<T>(this IEnumerable<T> source, int itemsPerGroup)

    {

        for(int i = 0; i < (int)Math.Ceiling( (double)source.Count() / itemsPerGroup ); i++)

        {

            var currentGroup = new Grouping<int,T>{ Key = i };

            currentGroup.AddRange(source.Skip(itemsPerGroup*i).Take(itemsPerGroup));

            yield return currentGroup;

        }

    }

    private class Grouping<TKey, TElement> : List<TElement>, IGrouping<TKey, TElement>

    {

        public TKey Key { get; set; }

    }

}

​