#include <stdio.h>

#include <math.h>

double len(int x1, int y1, int x2, int y2)
{
    return sqrt((double)(x2 - x1) * (x2 - x1) + (double)(y2 - y1) * (y2 - y1));
}

int main()
{
    int q, w, e, r, t, y;

    while (scanf("%d%d%d%d%d%d", &q, &w, &e, &r, &t, &y) != EOF)
    {
        double a = len(q, w, e, r);
        double b = len(q, w, t, y);
        double c = len(e, r, t, y);

        double p = (a + b + c) / 2;

        printf("%.2f\n", sqrt(p * (p - a) * (p - b) * (p - c)));
    }

    return 0;
}