RSOJava#6

import java.util.Scanner;
import java.lang.Math;

public class MyClass {
    public static void main(String args[]) {

        Scanner input = new Scanner(System.in);

        double area = input.nextDouble();

        if(area<=0){
            System.out.println("Area cannot be 0 or lower than 0...");
        } else{
            double radius = Math.sqrt(area/Math.PI);
            System.out.println("Circle radius is "+ radius);
        }
    }
}