题解 | 单组_spj判断浮点误差

import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner sc  = new Scanner(System.in);
        int r  = sc.nextInt();

        sc.close();
        double area = r*r*Math.PI;
        System.out.println(String.format("%.10f",area));
    }
}