#include<stdio.h>
#include<math.h>
int main()
{
double x1,y1,x2,y2,x3,y3,d1,d2,d3,s,w;
scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
d1=sqrt(pow(x1-x2,2)+pow(y1-y2,2));
d2=sqrt(pow(x1-x3,2)+pow(y1-y3,2));
d3=sqrt(pow(x3-x2,2)+pow(y3-y2,2));
w=(d1+d2+d3)/2;
s=sqrt(w*(w-d1)*(w-d2)*(w-d3));
printf("%.2f",w);
}