using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(ConvertAlphanumericPhoneNumber("1-800-500-4SKM"));

    }

     public static string ConvertAlphanumericPhoneNumber(string num)

       {

​

           var dict = new Dictionary<string, char>();

           dict.Add("abcABC", '2');

           dict.Add("defDEF", '3');

           dict.Add("ghiGHI", '4');

           dict.Add("jklJKL", '5');

           dict.Add("mnoMNO", '6');

           dict.Add("pqrsPQRS", '7');

           dict.Add("tuvTUV", '8');

           dict.Add("wxyzWXYZ", '9');

           foreach (var c in num.Where(f=> char.IsLetter(f)).ToList())

           {

               //Console.WriteLine(c);

               var digit = dict.First(d => d.Key.Contains(c)).Value;

               num = num.Replace(c, digit);

           }

 //Console.WriteLine(num);

           return num;

       }

}