お誕生日おめでとう！

HappyBirthday.cs

using System;
using System.Linq;

public class HappyBirthday
{
    public static void ShowHappyBirthday()
    {
        Console.WriteLine(string.Concat("Happy Birthday!".Select(x => new String(x, 3))));
    }
}

output.txt

HHHaaappppppyyy   BBBiiirrrttthhhdddaaayyy!!!