题解 | #单组_spj判断浮点误差#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int r = scanner.nextInt();
        double area = Math.PI * r * r;
        System.out.println(String.format("%.6f", area));
        scanner.close();
    }
}