#include <stdio.h>
#include<math.h>
int main(void) {
	// your code goes here
	float a,b,c,s,area;
	printf("Input a,b,c:");
	scanf("%f,%f,%f",&a,&b,&c);
	s=0.5*(a+b+c);
	area=(float)sqrt(s*(s-a)*(s-b)*(s-c));
	printf("area=%f\n",area);
	return 0;
}