import java.util.Scanner;

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

public class Main{
  public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    
    double R = Double.parseDouble(sc.nextLine());
    
    System.out.println(2 * R * Math.PI);
    
  }
}