using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string strText = "1234567890" + 

                         "ABCDEFGHIJ" + 

                         "1234567890" + 

                         "abcdefghij" + 

                         "1234567890";

        const int qtdQuebra = 10;

        var s = strText.Select((e, i) => ((i + 1) % qtdQuebra == 0) ? e + Environment.NewLine : e.ToString());  

        Console.WriteLine(string.Join("", s));

    }

}