#include <math.h>
#include <stdio.h>

int main()
{
    float
        x1, y1,
        x2, y2,
        x3, y3;
    scanf("%f%f%f%f%f%f", &x1, &y1, &x2, &y2, &x3, &y3);

    printf("S = %.3f\n", fabs((x1 - x3) * (y2 - y3) - (x2 - x3) * (y1 - y3)) / 2);

}