#include <iostream>
#include <cmath>

using namespace std;

double tArea(double ax,double ay,double bx,double by,double cx,double cy)
{
    double t=abs( (ax-cx)*(by-ay)-(ax-bx)*(cy-ay) )/2; 
    return t;
}
int main()
{
   cout << tArea(20,10,20,50,50,10) << endl; // 600
   
   return 0;
}