#include<stdio.h>
#include<math.h>
int main()
{
	int x0, y0, x1, y1, x2, y2;
	while (scanf("%d%d%d%d%d%d", &x0, &y0, &x1, &y1, &x2, &y2) != EOF)
	{
		double a = sqrt(pow(x1 - x0, 2) + pow(y1 - y0, 2));
		double b = sqrt(pow(x2 - x0, 2) + pow(y2 - y0, 2));
		double c = sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));//求三角形各边长度
		double p = (a + b + c) / 2;
		double s = sqrt(p * (p - a) * (p - b) * (p - c));//海伦公式 S=√p(p-a)(p-b)(p-c)
		printf("%0.2lf\n", s);
	}
	return 0;

}