//海伦公式
#include<bits/stdc++.h>
using namespace std;
int main(){
	double a[6];
	int i;
	double x,y,z,p,ans;
	while (cin >> a[0] >> a[1] >> a[2] >> a[3] >> a[4] >> a[5]) {
		x = sqrt(pow(a[0]-a[2],2)+pow(a[1]-a[3],2));
		y = sqrt(pow(a[0]-a[4],2)+pow(a[1]-a[5],2));
		z = sqrt(pow(a[2]-a[4],2)+pow(a[3]-a[5],2));
		p = (x + y + z)/2;
		ans = sqrt(p*(p-x)*(p-y)*(p-z));
		printf("%.2f\n",ans);
	}

	return 0;

}