import java.util.Scanner;

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

public class Main {
  
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int is = scan.nextInt();
    
    System.out.println((double)is * 2 * Math.PI);
    scan.close();
  }
}