#include <stdio.h>
int main(){
    double x1,y1,x2,y2,x3,y3,s;
    while(1){
        scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
        if(x1==0&&x2==0&&x3==0&&y1==0&&y2==0&&y3==0)break;
        s=0.5*(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2));
        if(s<0)s=-s;
        printf("%.1f\n",s);
    }
}