纯数学题 

#include <iostream>
using namespace std;

double a[2], b[2], c[2];

int main()
{
	while (cin >> a[0] >> a[1] >> b[0] >> b[1] >> c[0] >> c[1])
	{
		double tmp = a[0] * b[1] - a[0] * c[1] + b[0] * c[1] - b[0] * a[1] + c[0] * a[1] - c[0] * b[1];
		printf("%.2lf\n", 0.5 * (tmp > 0 ? tmp : -tmp));
	}
	return 0;
}