#include<cstdio>
#include<cmath>
int main(void)
{
    
    
	double ax=2.3;
	double ay=2.5;
	double bx=6.4;
	double by=3.1;
	double cx=5.1;
	double cy=7.2;
	double sum1,sum2,sum3;
	sum1=sqrt( pow(fabs(ax-bx),2) + pow(fabs(ay-by),2) ); 
	sum2=sqrt( pow(fabs(ax-cx),2) + pow(fabs(ay-cy),2) ); 
	sum3=sqrt( pow(fabs(cx-bx),2) + pow(fabs(cy-by),2) );
	double p=(sum1+sum2+sum3)/2; 
	double sum=sqrt(p*(p-sum1)*(p-sum2)*(p-sum3));
	printf("%.03lf",sum);
	return 0;
}