#include <cmath>
#include <iostream>
using namespace std;
class point{
public:
double x,  y;
point(){};
point(double x1, double y1){
x = x1;
y = y1;
}
};
double dist(point A, point B){
return sqrt( (A.x - B.x) * (A.x - B.x) + (A.y - B.y) * (A.y - B.y) );
}
const double pi = 3.14159265359;
int main(){
point a1, b1, c1;
cin >> a1.x >> a1.y >> b1.x >> b1.y >> c1.x >> c1.y;
double a, b, c;
a = dist(b1, c1);
b = dist(a1, c1);
c = dist(a1, b1);

double aarea = (a/2) * (a/2) * pi / 2;
double barea = (b / 2) * (b/2) * pi / 2;
double carea = (c / 2) * (c / 2) * pi / 2;
double brat = b / a;
double crat = c / a;
cout << barea + carea - (crat * crat + brat * brat) * aarea;
return 0;
}