#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>using namespace std;struct Point{ double x, y; Point operator -(const Point &b) { Point ret; ret.x = this->x - b.x; ret.y = this->y - b.y; return ret; }}p1, p2, p0;double xmult(Point a, Point b){ return a.x * b.y - a.y * b.x;}double mol(Point a){ return sqrt(a.x * a.x + a.y * a.y);}int main(){ while (~scanf("%lf%lf%lf%lf%lf%lf", &p0.x, &p0.y, &p1.x, &p1.y, &p2.x, &p2.y)) { Point a = p1 - p0; Point b = p2 - p0; Point c = p1 - p2; double R2 = abs(mol(c) / (xmult(a, b) / mol(a) / mol(b))); printf("%.2fn", R2 * 3.141592653589793); } return 0;}
