题解 | 单组_spj判断浮点误差

import java.util.Scanner;
import java.math.*;

// 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 in = new Scanner(System.in);
        int n = in.nextInt();
        BigDecimal s = new BigDecimal(n*n*(Math.PI));
        s = s.setScale(6,RoundingMode.HALF_UP);
        System.out.println(s.toPlainString());
        
        in.close();
    }
}