Append Binary Number to 4k digits where k is natural number

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace _6.BinToHex
{
    class BinToHex
    {
        static void Main(string[] args)
        {
            string binNumber = Console.ReadLine();
            string result = "";

            for (int i = 0; i < binNumber.Length; i+=4)
            {
                int binaryNumberLength = binNumber.Length;
                if (binNumber.Length % 4 != 0)
                {
                    //Пример 5 -> 5 % 4 = 1 => 5 + (4 - 1) = 8
                    int binaryNumberTotalLength =
                        binaryNumberLength + 4 - binaryNumberLength % 4;
                    binNumber = binNumber.PadLeft(binaryNumberTotalLength, '0');
                }
                switch (binNumber.Substring(i, 4))
                {
                    case "0000":
                        result += "0";
                        break;
                    case "0001":
                        result += "1";
                        break;
                    case "0010":
                        result += "2";
                        break;
                    case "0011":
                        result += "3";
                        break;
                    case "0100":
                        result += "4";
                        break;
                    case "0101":
                        result += "5";
                        break;
                    case "0110":
                        result += "6";
                        break;
                    case "0111":
                        result += "";
                        break;
                    case "1000":
                        result += "8";
                        break;
                    case "1001":
                        result += "9";
                        break;
                    case "1010":
                        result += "A";
                        break;
                    case "1011":
                        result += "B";
                        break;
                    case "1100":
                        result += "C";
                        break;
                    case "1101":
                        result += "D";
                        break;
                    case "1110":
                        result += "E";
                        break;
                    case "1111":
                        result += "F";
                        break;
                    default:
                        result += "";
                        break;
                }
            }
            Console.WriteLine(result);
        }
    }
}