using System;
using System.Text;
using static System.Convert;

public class Test
{
	public static void Main()
	{
		const string input = "thi";
		var encoded = ToBase64String(Encoding.UTF8.GetBytes(input));
		Console.WriteLine(encoded);
		var decoded = Encoding.UTF8.GetString(FromBase64String(encoded));
		Console.WriteLine(decoded);
	}
}