import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   }
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   }
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   } main {
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) float R = sc.nextInt(); R sc.nextInt() sc.nextInt sc System.out.println(R*2*3.14) System.out.println System.out System System.out R*2*3.14 R*2*3.14 R 2 3.14 String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   }
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   }
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		float R = sc.nextInt();
      System.out.println(R*2*3.14);
   }
}
