BinToHex

using System;
using System.Text;

class ConvertBinToHex
{
    static void Main()
    {
        string s = Console.ReadLine();

        while (s.Length % 4 != 0)
        {
            s = '0' + s;
        }
        StringBuilder hexRepresent = new StringBuilder();
        for (int i = 0; i < s.Length; i+=4)
        {
            string subStr = s.Substring(i, 4);
            switch (subStr)
            {
                case "1010": hexRepresent.Append('A'); break;
                case "1011": hexRepresent.Append('B'); break;
                case "1100": hexRepresent.Append('C'); break;
                case "1101": hexRepresent.Append('D'); break;
                case "1110": hexRepresent.Append('E'); break;
                case "1111": hexRepresent.Append('F'); break;
                case "0001": hexRepresent.Append('1'); break;
                case "0010": hexRepresent.Append('2'); break;
                case "0011": hexRepresent.Append('3'); break;
                case "0100": hexRepresent.Append('4'); break;
                case "0101": hexRepresent.Append('5'); break;
                case "0110": hexRepresent.Append('6'); break;
                case "0111": hexRepresent.Append('7'); break;
                case "1000": hexRepresent.Append('8'); break;
                case "1001": hexRepresent.Append('9'); break;
                case "0000": hexRepresent.Append('0'); break;
                default:
                    break;
            }
        }
        Console.WriteLine(hexRepresent);
    }
}