#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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