import java.util.Scanner;

public class AlcoholMarket {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        // read input
        //caluclate wine price

        double whiskeyPricePerLiter = Double.parseDouble(scanner.nextLine());
        double beerLeters = Double.parseDouble(scanner.nextLine());
        double wineLeters = Double.parseDouble(scanner.nextLine());
        double rakiaLiters = Double.parseDouble(scanner.nextLine());
        double whiskeyLiters = Double.parseDouble(scanner.nextLine());


        double rakiaPricePerLiter = whiskeyPricePerLiter - whiskeyPricePerLiter * 0.5;
        double winePricePerLiter = rakiaPricePerLiter - rakiaPricePerLiter * 0.4;
        double beerPricePerLiter = rakiaPricePerLiter - rakiaPricePerLiter * 0.8;
        double totalPrice = whiskeyPricePerLiter * whiskeyLiters
                + whiskeyPricePerLiter * wineLeters
                + beerPricePerLiter * beerLeters
                + rakiaPricePerLiter * rakiaLiters;

        System.out.printf("%.2f", totalPrice);
    }
}