using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var paragraph = "Please change the format: 112-344-423";

        var subStr2 = paragraph.Substring(26).Replace("-", "");

        Console.WriteLine(subStr2);

        var arr = subStr2.Insert(2,"/").Insert(7,"/");

        Console.WriteLine(arr);

​

    }

}