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