using System;

public class Program

{

    public static void Main()

    {

        double priceForV = double.Parse(Console.ReadLine());

        double priceForF = double.Parse(Console.ReadLine());

        int kgV = int.Parse(Console.ReadLine());

        int kgF = int.Parse(Console.ReadLine());

        double price = (priceForV * kgV + priceForF * kgF) / 1.94;

        Console.WriteLine(Math.Round(price, 2));

    }

}