using System;

using System.Numerics;

​

public class Program

{

    public static void Main()

    {

        var s = "1234567890123456789012";

        Console.WriteLine("{0}: {1}", s.Length, s);

        s = System.Convert.ToBase64String(BigInteger.Parse(s).ToByteArray());

        Console.WriteLine("{0}: {1}", s.Length, s);

    }

}