using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _01.VegetableMarket
{
    class Program
    {
        static void Main(string[] args)
        {
            var priceFor1KiloVegetables = double.Parse(Console.ReadLine());
            var priceFor1KiloFruits = double.Parse(Console.ReadLine());
            var totalKilosOfVegetables = int.Parse(Console.ReadLine());
            var totalKilosOfFruits = int.Parse(Console.ReadLine());

            var priceOfVegetables = priceFor1KiloVegetables * totalKilosOfVegetables;
            var priceOfFruits = priceFor1KiloFruits * totalKilosOfFruits;
            var totalPriceBGN = priceOfVegetables + priceOfFruits;
            var totalPriceEURO = totalPriceBGN / 1.94;
            Console.WriteLine(totalPriceEURO);
        }
    }
}