import java.util.Scanner;

public class Main{
public static void main(String[]args){
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 }
 } import java.util.Scanner; Scanner java.util public class Main{
public static void main(String[]args){
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 }
 } Main public static void main(String[]args){
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 } main {
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 } final double PI = 3.141592; PI 3.141592 Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) double r = stdIn.nextDouble(); r stdIn.nextDouble() stdIn.nextDouble stdIn System.out.println(2 * PI * r ) System.out.println System.out System System.out 2 * PI * r 2 * PI * r 2 PI r String[]args args public class Main{
public static void main(String[]args){
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 }
 } public class Main{
public static void main(String[]args){
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 }
 } Main
import java.util.Scanner;

public class Main{
public static void main(String[]args){
  final double PI = 3.141592;
  Scanner stdIn = new Scanner(System.in);
  double r = stdIn.nextDouble();
  System.out.println(2 * PI * r );

 }
 }