import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  } main {
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) Double R = sc.nextDouble(); R sc.nextDouble() sc.nextDouble sc R=2*R*3.141592653589793238462 R 2*R*3.141592653589793238462 2*R*3.141592653589793238462 2 R 3.141592653589793238462 System.out.println(R) System.out.println System.out System System.out R String[] args args public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  }
} Main
import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
 
    Double R = sc.nextDouble();
    R=2*R*3.141592653589793238462;
    System.out.println(R);
 
 
  }
}