import java.util.Scanner;

public class AlcoholMarket {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        double lenght = Double.parseDouble(scanner.nextLine());
        double wight = Double.parseDouble(scanner.nextLine());
        double bar =  Double.parseDouble(scanner.nextLine());

        double zala = lenght * wight;
        double barSize = bar * bar;
        double dance = zala*0.19;
        double freeSpace =zala-barSize-dance;
        double peaple= freeSpace/3.2;
        System.out.printf("%.1f",Math.ceil(peaple));

    }
}