#include <iostream.h>
{
  private:
float r,
;

  public:
  circle_area();
};
float circle::circle_area(float r)
{
   return 4*PAI*r*r;
}
   void main()
   {   
   float PAI=3.14;
    int s;
circle mycircle;
cin>>r;
s=circle_area();
cout<<"s= "<<s<<endl;
   }