using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var codigoInicial = "EMP2-SUS-ANC-1001";

        var index = codigoInicial.LastIndexOf("-") +1;

        var codigo = codigoInicial.Substring(0, index).Replace("ANC", "RNC") + 12360.ToString().PadLeft(4, '0');

        //The Count is an extension method introduced by LINQ that loops over all the items 

        Console.WriteLine(codigo); 

​

    }

}