package io;

import java.io.*;

public class CircleArea {
	public static void main(String[] args) {		
			BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
			System.out.print("請輸入圓的半徑：");
			try {
				double r=Double.parseDouble(br.readLine());
				double area=0;
				if(r>=0){
					area=Math.PI*Math.pow(r, 2);
					System.out.println("圓的面積為"+area);
				}else{
					System.err.println("輸入半徑不合法。");
				}				
			} catch (NumberFormatException e) {
				e.printStackTrace();
			} catch (IOException e) {				
				e.printStackTrace();
			}		
	}
}