import java.util.Scanner;
 
public class Main {
  
  private static double p = 2 * Math.PI;
 
    public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    }
} import java.util.Scanner; Scanner java.util public class Main {
  
  private static double p = 2 * Math.PI;
 
    public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    }
} Main private static double p = 2 * Math.PI; p 2 * Math.PI 2 Math.PI Math Math.PI public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    } main {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    } Scanner in = new Scanner(System.in); in new Scanner(System.in) int r = in.nextInt(); r in.nextInt() in.nextInt in in.close() in.close in System.out.println(p * r) System.out.println System.out System System.out p * r p r String[] args args public class Main {
  
  private static double p = 2 * Math.PI;
 
    public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    }
} public class Main {
  
  private static double p = 2 * Math.PI;
 
    public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    }
} Main
import java.util.Scanner;
 
public class Main {
  
  private static double p = 2 * Math.PI;
 
    public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      int r = in.nextInt();
        
      in.close();
      
      System.out.println(p * r);
    }
}