#include <stdio.h>
#include <math.h>
int main(void) {
	// your code goes here
    double a,b,c,s,area;
    scanf("%lf,%lf,%lf",&a,&b,&c);
    s=(a+b+c)/2;
    area=(float)sqrt(s*(s-a)*(s-b)*(s-c));
    printf("area=%f",area);
	return 0;
}