Convert binary to hex

using System;
using System.Text;
//Write a program to convert binary numbers to hexadecimal numbers (directly).
class BinaryToHex
{
    static void Main()
    {
        Console.WriteLine("Enter binary number : ");
        string convert = Console.ReadLine();
        StringBuilder builder = new StringBuilder();

        builder.Append(convert);
        while (convert.Length%4 != 0) //inset with zeros
        {
            builder.Insert(0, 0);
            convert = builder.ToString();
        }
        builder.Clear();

        int temp = 0;
        for (int i = 0; i < convert.Length; i+=4)
        {
            temp = 0;
            for (int j = 0, reverse = 3; j <= 3; j++, reverse--)
            {
                if (convert[i + j] == '1')
                {
                    temp += (int)Math.Pow(2, reverse);
                }
            }

            if (temp > 9)
            {
                switch (temp)
                    {
                        case 10: builder.Append('A'); break;
                        case 11: builder.Append('B'); break;
                        case 12: builder.Append('C'); break;
                        case 13: builder.Append('D'); break;
                        case 14: builder.Append('E'); break;
                        case 15: builder.Append('F'); break;
                    }
            }
            else
            {
                builder.Append(temp);
            }
        }

        Console.WriteLine("Converted number: \n{0}",builder.ToString());
    }
}