using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<string> s = new List<string>() { "a", "b", "c", "a"};

        var asc = s.OrderBy(e => e).ToList<string>();

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

    }

}