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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalculateCircleArea {

public static void main(String[] args) {

int radius = 0;
System.out.println("Please enter the radius of a circle");

try
{
//get the radius from user
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
radius = Integer.parseInt(br.readLine());
}
//if invalid value was entered
catch(NumberFormatException ne)
{
System.out.println("Invalid radius value" + ne);
System.exit(0);
}
catch(IOException ioe)
{
System.out.println("IO Error :" + ioe);
System.exit(0);
}

/*
* Area of a circle = pi * r * r
* where r is a radius of a circle.
*/

//NOTE : use Math.PI constant to get value of pi
double area = Math.PI * radius * radius;

System.out.println("Area of a circle is " + area);
}
}