import java.util.Scanner;
public class Hello {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("为半径输入一个数值");
double banjing=input.nextDouble();
double area=banjing*banjing*Math.PI;
System.out.println("半径为"+banjing+"的圆的面积是"+area);
}
}