using System;
using System.Text.RegularExpressions;
using System.IO;
public class Test
{
	public static void Main()
	{
		var data = new string[] {"(123) 556-7890", "123 556 7890", "(123) 556- 7890"};
		foreach (var s in data) {
			Console.WriteLine(Regex.Replace(s, @"\d(?!\d{0,3}$)", "X"));
		}
	}
}