#include<stdio.h>
#include<math.h>

int main()
{   
	float a,b,c,area,s;
	scanf("%f %f %f",&a,&b,&c);
	s = (a + b + c) / 2;
	area = sqrt(s * (s - a) * (s - b) * (s-c));
	printf("area = %.2f",area);
    return 0;
}