#include <iostream>
using namespace std;
int main(){
	double x1,x2,x3,y1,y2,y3;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	double sum=((x1*y2-x2*y1)+(x2*y3-x3*y2)+(x3*y1-x1*y3));
    sum/=2;
	if(sum>0)
        cout <<sum;
	else
	    cout <<0-sum;
	cout <<endl;
	return 0;
}

include

using namespace std; int main(){ double x1,x2,x3,y1,y2,y3; cin>>x1>>y1>>x2>>y2>>x3>>y3; double sum=((x1y2-x2y1)+(x2y3-x3y2)+(x3y1-x1y3)); sum/=2; if(sum>0) cout <<sum; else cout <<0-sum; cout <<endl; return 0; }