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