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