using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(HexToByte("7201ad3ecc033bfe1019dc7be802f988").Length);

    }

     private static byte[] HexToByte(string thisString)

        {

            var temp = new byte[thisString.Length / 2];

            var hexValue = new[]

                                 {

                                     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,

                                     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0A, 0x0B, 0x0C, 0x0D,

                                     0x0E, 0x0F

                                 };

            for (int x = 0, i = 0; i < thisString.Length; i += 2, x += 1)

            {

                temp[x] = (byte)(hexValue[Char.ToUpper(thisString[i + 0]) - '0'] << 4 |

                                  hexValue[Char.ToUpper(thisString[i + 1]) - '0']);

            }

​

            return temp;

        }

}