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


class Vegetable
{
    static void Main(string[] args)
    {
        double priceVegetable = double.Parse(Console.ReadLine());
        double priceFruit = double.Parse(Console.ReadLine());
        int kgVegetable = int.Parse(Console.ReadLine());
        int kgFruit = int.Parse(Console.ReadLine());
        double first = (priceVegetable * kgVegetable) / 1.94;
        double second = (priceFruit * kgFruit) / 1.94;
        double resul = first + second;
        Console.WriteLine("{0}", resul);
    }
}