using System;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var s = "cC-Cc";
		var result = Regex.Replace(s, @"(?i)^([a-z]{2})-([a-z]{2})$", m => 
    		$"{m.Groups[1].Value.ToLower()}-{m.Groups[2].Value.ToUpper()}");
        Console.WriteLine(result);
	}
}