import java.util.Scanner;

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

        double length = Double.parseDouble(sc.nextLine());
        double width = Double.parseDouble(sc.nextLine());
        double barSide = Double.parseDouble(sc.nextLine());

        double hallSize = length*width;
        double barSize = barSide*barSide;

        double dancingSize = hallSize*0.19;
        double freeSpace = hallSize - (barSize + dancingSize);

        double guests = Math.ceil(freeSpace/3.2);

        System.out.printf("%.0f", guests);
    }
}