#include <stdio.h>
#include<math.h>
int main(void)
{
   float a,b,c,s,area;
   printf("Input a,b,c:");
   scanf("%f,%f,%f",&a,&b,&c);
   s=(a+b+c)/2;
   area=(float)sqrt(s*(s-a)*(s-b)*(s-c));
   printf("area=%f\n",area);
	return 0;
}