import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	} main {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int r = scan.nextInt(); r scan.nextInt() scan.nextInt scan double length = 2.0 * r * Math.PI; length 2.0 * r * Math.PI 2.0 * r * Math.PI 2.0 r Math.PI Math Math.PI System.out.println(length) System.out.println System.out System System.out length String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double length = 2.0 * r * Math.PI;
		System.out.println(length);
	}
}