#include <stdio.h>
#include <math.h>
int main()
{//用float设x，结果会有零点几的误差
	double x1,x2,x3,y1,y2,y3,a=0,b=0,c=0,sum=0,i=0;
	scanf("%lf %lf %lf %lf %lf %lf",
	&x1,&y1,&x2,&y2,&x3,&y3);
	a=sqrt(pow(x2-x1,2)+pow(y2-y1,2));
	b=sqrt(pow(x3-x1,2)+pow(y3-y1,2));
    c=sqrt(pow(x2-x3,2)+pow(y2-y3,2));
    i=(a+b+c)/2.0;
	sum=sqrt(i*(i-a)*(i-b)*(i-c));
	printf("%.2f",sum);
	return 0;
}