import java.util.Scanner;


public class Demo1
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        double  radius;
        double  area;

        System.out.print("Enter a radius: ");
        radius = input.nextDouble();
 
        if ( radius >= 0 )
        {
            // Compute and print area ONLY when radius >= 0

            area = 3.14159 * radius * radius;
            System.out.println(area);
        }
   }                       
}