circlearea

import java.util.Scanner;

public class circlearea {

	public static void main (String [] args) {

		Scanner input = new Scanner(System.in);

		int radius = input.nextInt();

		double area = areaofcirc(radius);

		System.out.println(area);


		}

	public static double areaofcirc (int radius){

		double area = radius*2;
		area = area* Math.PI;

		return area;
	}

}