java
包

import java.text.DecimalFormat;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        double e = in.nextDouble();
        DecimalFormat df = new DecimalFormat("0.0000");
        e = 3.14159 * e * e ;
        System.out.println("A=" + df.format(e));
    }
}