using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(TraduireNumTel("Jean Pierre 444444 3333"));

    }

​

    private static string TraduireNumTel(string numCell)

        => Regex.Replace(numCell, "(\\d{3})(\\d{3})(\\d{4})", "$1 $2-$3");

}