#include<iostream> #include<cmath> using namespace std; #define pi 3.141592653589793 int main() { double x1,y1,x2,y2,x3,y3,a,b,c,l,s,r,L; while(cin>>x1>>y1>>x2>>y2>>x3>>y3) { a=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)); b=sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1)); c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3)); l=(a+b+c)/2; s=sqrt(l*(l-a)*(l-b)*(l-c)); r=(a*b*c)/(4*s); L=2*pi*r; printf("%.2f\n",L); } return 0; }

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