Vending Mchine

using System;

namespace vendingMachine
{
    class Program
    {
        static void Main()
        {
            string money = Console.ReadLine();
            double sum = 0.0;
            while (money != "Start")
            {
                double coin = double.Parse(money);
                switch (coin)
                {
                    case 0.1:
                    case 0.2:
                    case 0.5:
                    case 1:
                    case 2:
                        sum += coin;
                        break;
                    default:
                        Console.WriteLine($"Cannot accept {coin}");
                        break;
                }
                money = Console.ReadLine();
            }
            string product = Console.ReadLine();
            double productPrice = 0;
            bool isValid = true;
            while (product != "End")
            {
                switch (product)
                {
                    case "Nuts": productPrice = 2;
                        break;
                    case "Water": productPrice = 0.7;
                        break;
                    case "Crisps": productPrice = 1.5;
                        break;
                    case "Soda": productPrice = 0.8;
                        break;
                    case "Coke": productPrice = 1;
                        break;
                    default: Console.WriteLine("Invalid product");
                        isValid = false;
                        break;
                }
                if (sum >= productPrice && isValid == true)
                {
                    Console.WriteLine($"Purchased {product.ToLower()}");
                    sum -= productPrice;
                }
                else if (isValid == true)
                {
                    Console.WriteLine($"Sorry, not enough money");
                }
                product = Console.ReadLine();

            }
            Console.WriteLine($"Change: {sum:f2}");
        }
    }
}