import java.util.Scanner;

public class Exam3_3_10_2018_WeddingHall {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        double hallLengthCm = Double.parseDouble(scanner.nextLine());
        double hallWidthCm = Double.parseDouble(scanner.nextLine());
        double barSideCm = Double.parseDouble(scanner.nextLine());

        int hallArea = (int) (hallLengthCm * hallWidthCm);
        int barSideArea = (int) (barSideCm * barSideCm);
        double danceFloorArea = hallArea * 0.19;
        double freeSpace = hallArea - danceFloorArea - barSideArea;

        int numberGuests = (int) Math.ceil(freeSpace/ 3.2);

        System.out.println(numberGuests);
    }
}