0分，求条，必关！

#include<bits/stdc++.h>
using namespace std;
double mianji(double x1,double y1,double x2,double y2,double x3,double y3){
	return fabs((x1*y2+x2*y3+x3*y1-x1*y3-x2*y1-x3*y2)/2.0);
}
int main(){
	double x1,y1,x2,y2,x3,y3;
    printf("%.2lf",mianji(x1,y1,x2,y2,x3,y3));
	return 0;
}