using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var input = "+15559999000";

        input=Regex.Replace(input,"\\+1([0-9]{3})([0-9]{3})([0-9]{4})", "$1-$2-$3");

        Console.WriteLine(input);

    }

}