using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(updatePhone("3786446"));

        Console.WriteLine(updatePhone("5093786446"));

        Console.WriteLine(updatePhone("15093786446"));

        Console.WriteLine(updatePhone("+15093786446"));

    }

    private static string updatePhone(string phoneNumber)

    {

        //used to add '-' to phone number in reports

        var builder = new StringBuilder();

        var count = 0;

        foreach (var character in phoneNumber)

        {

            builder.Append(character);

            if((++count % 8) == 0)

            {

                builder.Append('-');

            }

        }

        return builder.ToString();

    }

}