import java.util.Scanner; 

class Main{

 public static void main(String[] args){

 Scanner scan = new Scanner(System.in);

 int R = scan.nextInt();
 double a= 6.28318530717958623200;
 double number=a*R;

System.out.println(number);

 }
} import java.util.Scanner; Scanner java.util class Main{

 public static void main(String[] args){

 Scanner scan = new Scanner(System.in);

 int R = scan.nextInt();
 double a= 6.28318530717958623200;
 double number=a*R;

System.out.println(number);

 }
} Main public static void main(String[] args){

 Scanner scan = new Scanner(System.in);

 int R = scan.nextInt();
 double a= 6.28318530717958623200;
 double number=a*R;

System.out.println(number);

 } main {

 Scanner scan = new Scanner(System.in);

 int R = scan.nextInt();
 double a= 6.28318530717958623200;
 double number=a*R;

System.out.println(number);

 } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int R = scan.nextInt(); R scan.nextInt() scan.nextInt scan double a= 6.28318530717958623200; a 6.28318530717958623200 double number=a*R; number a*R a R System.out.println(number) System.out.println System.out System System.out number String[] args args
import java.util.Scanner; 

class Main{

 public static void main(String[] args){

 Scanner scan = new Scanner(System.in);

 int R = scan.nextInt();
 double a= 6.28318530717958623200;
 double number=a*R;

System.out.println(number);

 }
}