01. Computer Store

using System;

namespace ComputerStore
{
    class Program
    {
        static void Main(string[] args)
        {
            double totalPrice = 0, price;

            string command = Console.ReadLine();

            while (command != "special" && command != "regular")
            {
                price = double.Parse(command);

                if (price > 0)
                {
                    totalPrice += price;
                }
                else
                {
                    Console.WriteLine("Invalid price!");
                }
                command = Console.ReadLine();
            }

            if (totalPrice == 0)
            {
                Console.WriteLine("Invalid order!");
            }
            else
            {
                Console.WriteLine(
                    $"Congratulations you've just bought a new computer!\n" +
                    $"Price without taxes: {totalPrice:f2}$\n" +
                    $"Taxes: {totalPrice / 5:f2}$\n" +
                    $"-----------\n" +
                    $"Total price: {totalPrice * 1.2 * (command == "special" ? 0.9 : 1):f2}$"
                    );
            }
        }
    }
}