using System;

namespace Vegetable_Market
{
    class Program
    {
        static void Main(string[] args)
        {
            double kgVegetables = double.Parse(Console.ReadLine());
            double kgFrutis = double.Parse(Console.ReadLine());
            double vegetables = double.Parse(Console.ReadLine());
            double frutis = double.Parse(Console.ReadLine());

            double EUR = 1.94;

            double priceVegetables = kgVegetables * vegetables;
            double priceFruties = kgFrutis * frutis;

            double totalPrice = priceVegetables + priceFruties / EUR;

            Console.WriteLine($"{totalPrice:F2}");

        }
    }
}