import java.util.*;

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

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