import java.util.*;
class Main{
    public static void main(String[] args){
        Scanner s=new Scanner(System.in);
        float r=s.nextFloat();
        if(r<0){
            System.out.print("Invalid input");
            return;
        }
        double res=3.14159*r*r;
        System.out.print("%.2f",res);
        
    }
}