#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
double junk(double x,double y)
{
double s=sqrt(x*x+y*y);
return 0;
{
double x1,x2,x3,y1,y2,y3;
cin>>x1>>x2>>x3>>y1>>y2>>y3;
double a=junk(x1-x2,y1-y2),b=junk(x2-x3,y2-y3),c=junk(x3-x1,y3-y1);
double p=(a+b+c)/2;
double s=sqrt(p*(p-a)*(p-b)*(p-c));
printf("%.2f",s);
return 0;
}
}