public class Area{
	public static void main(String[] args){
		double a = 3.0;
		double b = 4.0;
		double c = 5.0;
		double s = 0.0;
		double area;

		s = (a+b+c)/2;
		area = Math.sqrt(s*(s-a)*(s-b)*(s-c));
		System.out.println(area);
}
}