#include <stdio.h>
#include<math.h>
int main(void){
    // you code goes here
    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;
}