import java.util.Scanner;

class Main{
 public static void main(String[] args){
  Scanner stdIn = new Scanner(System.in);
   final double pi = 3.141;
   int R = stdIn.nextInt();
   double Enshu = 2 * pi * R;
   
   System.out.println(Enshu);
 }
} import java.util.Scanner; Scanner java.util class Main{
 public static void main(String[] args){
  Scanner stdIn = new Scanner(System.in);
   final double pi = 3.141;
   int R = stdIn.nextInt();
   double Enshu = 2 * pi * R;
   
   System.out.println(Enshu);
 }
} Main public static void main(String[] args){
  Scanner stdIn = new Scanner(System.in);
   final double pi = 3.141;
   int R = stdIn.nextInt();
   double Enshu = 2 * pi * R;
   
   System.out.println(Enshu);
 } main {
  Scanner stdIn = new Scanner(System.in);
   final double pi = 3.141;
   int R = stdIn.nextInt();
   double Enshu = 2 * pi * R;
   
   System.out.println(Enshu);
 } Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) final double pi = 3.141; pi 3.141 int R = stdIn.nextInt(); R stdIn.nextInt() stdIn.nextInt stdIn double Enshu = 2 * pi * R; Enshu 2 * pi * R 2 * pi * R 2 pi R System.out.println(Enshu) System.out.println System.out System System.out Enshu String[] args args
import java.util.Scanner;

class Main{
 public static void main(String[] args){
  Scanner stdIn = new Scanner(System.in);
   final double pi = 3.141;
   int R = stdIn.nextInt();
   double Enshu = 2 * pi * R;
   
   System.out.println(Enshu);
 }
}