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#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
typedef struct point{
double x;
double y;
}point;
double CrossProduct(point A, point B, point C){
return (B.x-A.x)*(C.y-A.y) - (B.y-A.y)*(C.x-A.x);
}
int main()
{
point a, b, c;
double temp, area;
cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y;
temp = CrossProduct(a, b, c);
area = 0.5*fabs(temp);
cout << area << endl;
return 0;
}