#include <iostream.h> #define pi 3.141592653589793 #include <math.h> #include <fstream.h> ifstream f("circle.in"); #define cin f #include<iomanip.h> int main() {     //float a,b,c,d,e,f;     float x1,x2,x3,y1,y2,y3,x,y,r;     while(cin>>x1>>y1>>x2>>y2>>x3>>y3)     {         float k1,k2;         /*x1=(long)(a*10);         y1=(long)(b*10);         x2=(long)(c*10);         y2=(long)(d*10);         x3=(long)(e*10);         y3=(long)(f*10);         */                  if((int)(10*y1)!=(int)(10*y2) && (int)(10*y3)==(int)(10*y2))         {             k2=-(x1-x2)/(y1-y2);             x=(x3+x2)/2;             y=k2*(x-(x2+x1)/2)+(y2+y1)/2;         }         else if((int)(10*y1)==(int)(10*y2) && (int)(10*y3)!=(int)(10*y2))         {             k1=-(x3-x2)/(y3-y2);             x=(x1+x2)/2;             y=k1*(x-(x2+x3)/2)+(y2+y3)/2;         }         else         {             k1=-(x1-x2)/(y1-y2);             k2=-(x3-x2)/(y3-y2);                         x=(y3-y1+k1*(x1+x2)-k2*(x2+x3))/(k1-k2)/2;             y=k1*x+(y1+y2-k1*x1-k1*x2)/2;           }           //cout<<x<<"  "<<y<<endl;                     //else if((int)(10*y1)==(int)(10*y2))         //k1=1;         //else         //k1=-(x1-x2)/(y1-y2);         //if((int)(x3*10)==(int)(x2*10))         //k2=0;         //else if((int)(10*y3)==(int)(10*y2))         //k2=1;         //else         //k2=-(x3-x2)/(y3-y2);         //x=(y3-y1+k1*(x1+x2)-k2*(x2+x3))/(k1-k2)/2;         //y=k1*x-(y1+y2-k1*x1-k1*x2)/2;         r=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));         //cout<<2*pi*r<<endl;         cout.setf(ios::fixed);         cout<<setprecision(2)<<2*pi*r<<endl;             } }        

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