Hex to Dec only loops

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

namespace _15.HexadecimalToDecimal
{
    class HexadecimalToDecimal
    {
        static void Main()
        {
            Console.Write("Enter a number to convert to hexadecimal: ");
            string hex = Console.ReadLine();
            long dec = 0;
            long power = 1;
            for (int i = hex.Length - 1; i >= 0; i--)
            {
                int digitToNum = 0;
                switch (hex[i])
                {
                    case 'A':
                        digitToNum = 10;
                        break;
                    case 'B':
                        digitToNum = 11;
                        break;
                    case 'C':
                        digitToNum = 12;
                        break;
                    case 'D':
                        digitToNum = 13;
                        break;
                    case 'E':
                        digitToNum = 14;
                        break;
                    case 'F':
                        digitToNum = 15;
                        break;

                    default:
                        digitToNum = hex[i] - '0';
                        break;
                }
                dec += digitToNum * power;
                power *= 16;
            }
            Console.WriteLine(dec);
        }
    }
}