/**
 * Matt Kretchmar
 * January 17, 2006
 * CircleArea2.java
 * This program computes the area of a circle given its dimeter.
 */

import java.math.*;
import java.util.Scanner;

class CircleArea2
{   
    public static void main ( String [] args )
    {
        double diameter;
        double radius;
        double area;
        Scanner keyboard;
        
        keyboard = new Scanner(System.in);
        
        // Get input from user
        System.out.println("Enter the circle's diameter: ");
        diameter = keyboard.nextDouble();

        // area of a circle is pi*r^2
        radius = diameter / 2.0;
        area = Math.PI * radius * radius;
        
        System.out.println("The area of a circle with diameter " + 
          diameter + " is " + area + ".");
    }
}