using System;
namespace Fruit_Shop
{
    class fruit_shop
    {
        static void Main(string[] args)
        {
            var days = new [] {"monday", "tuesday", "wednesday", "thursday", "friday", "saturday", "sunday"};
            var fruits = new [] {"banana", "apple", "orange", "grapefruit", "kiwi", "pineapple", "grapes"};
            var regular_prices = new [] {2.50, 1.2, .85, 1.45, 2.7, 5.5, 2.85};
            var weekend_prices = new [] {2.7, 1.25, .9, 1.6, 3, 5.6, 4.2};

            var fruit = Console.ReadLine().ToLower();
            var day = Console.ReadLine().ToLower();
            var quantity = double.Parse(Console.ReadLine());

            var iday = Array.IndexOf(days, day);
            var ifruit = Array.IndexOf(fruits, fruit);

            if(iday == -1 || ifruit == -1)
                Console.WriteLine("error");
            else {
                var prices = iday < 5 ? regular_prices : weekend_prices;
                Console.WriteLine("{0:N2}", quantity*prices[ifruit]);
            }
        }
    }
}