02. Triangle Area

import java.util.Scanner;

public class T11 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        Double A = Double.parseDouble(scanner.nextLine());
        Double H = Double.parseDouble(scanner.nextLine());

        Double Area = (A*H) / 2;

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