using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        List<string> str = new List<string> { "1", "22", "3", "44", "55", "666666", "7777777", "8", "99" };

        int n = 5;

        var result = new List<string>();

        var last = str.Aggregate("",

                    (current, next) => 

                    {

                        var toBeAppended = current + next;

                        if (toBeAppended.Length >= n)

                        {

                            result.Add(current);

                            current = next;

                        }

                        else

                        {

                            current = toBeAppended;

                        }

                        return current; 

                    });

        result.Add(last);

        Console.WriteLine(JsonConvert.SerializeObject(result));

    }

}