#include<stdio.h>
#include<math.h>
int main(){
    double x1,y1,x2,y2,x3,y3;
    scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
    printf(".2lf",fabs((x2-x3)*(y1-y3)-(x1-x3)*(y2-y3))/2);
    return 0;}