using System;

using System.Collections.Generic;

public class Program

{

    public List<string> GetAlbums(List<string> files)

{

        var dir = new List<string>();

        for (int i=0; i<files.Count; i++)

            if (files[i].Substring(files[i].Length-3, 3) == "mp3" || files[i].Substring(files[i].Length-3, 3) == "wav")

                if (!(dir.Contains(files[i])))

                    dir.Add(files[i]);      

        return dir;

}

    public void Main()

    {

        var list = new List<string>() {"1.mp3", "2.wav", "1.mp3"};

        var temp = new List<string>();

        temp = GetAlbums(list);

        foreach (var e in temp)

        Console.WriteLine(e);

    }

}