<span style="background-color: rgb(255, 255, 255);"><span style="font-size:18px;"><span style="text-indent: 2em;">給定圓的半徑r，求圓的面積。</span>要求四捨五入保留小數點後7位。PI=atan(1.0)*4。</span></span>

import java.math.BigDecimal;
import java.util.Scanner;

public class Main
{
	public static void main(String[] args)
	{
		double PI = 3.14159265358979323;
		Scanner scanner = new Scanner(System.in);
		int r = scanner.nextInt();
		double d = 0;
		d = PI * r * r;
		BigDecimal decimal = new BigDecimal(d);
		BigDecimal b = decimal.setScale(7,BigDecimal.ROUND_HALF_UP);
		System.out.println(b.toPlainString());
		scanner.close();
	}
}
 

import java.util.Scanner;

public class Main
{
	public static void main(String[] args)
	{
		double PI = Math.atan(1.0)*4;
		Scanner scanner = new Scanner(System.in);
		int r = scanner.nextInt();
		String s = String.format("%.7f", PI * r * r);
		System.out.println(s);
		scanner.close();
	}
}