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