Java 代码

import java.util.Scanner;

public class Main
{
    static final double  PI = 3.14159;

    public static void main(String[] args)
    {
        Scanner cin = new Scanner(System.in);
        double r = cin.nextDouble();

        double A = PI * r * r;

        System.out.println ("A=" + String.format("%.4f", A));
    }
}