import java.util.*;

public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      }
      } import java.util.*; util.* java public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      }
      } Main public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      } main {
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc System.out.println(2*3.1415926*R) System.out.println System.out System System.out 2*3.1415926*R 2*3.1415926*R 2 3.1415926 R String[] args args public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      }
      } public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      }
      } Main
import java.util.*;

public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();

	System.out.println(2*3.1415926*R);
      }
      }
