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

public class Test
{
	public static void Main()
	{
		var s = "My name is Adam";
    	var result = Regex.Replace(s, @"(\p{Lu})|\S", m => 
        	m.Groups[1].Success ? "X" : "x");
       	Console.WriteLine(result);
	}
}