import java.util.*;
public class Main{

	public static void main(String[]args){
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    }

} import java.util.*; util.* java public class Main{

	public static void main(String[]args){
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    }

} Main public static void main(String[]args){
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    } main {
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) int t=sc.nextInt(); t sc.nextInt() sc.nextInt sc System.out.println(t*6.28318530717958623200) System.out.println System.out System System.out t*6.28318530717958623200 t 6.28318530717958623200 String[]args args public class Main{

	public static void main(String[]args){
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    }

} public class Main{

	public static void main(String[]args){
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    }

} Main
import java.util.*;
public class Main{

	public static void main(String[]args){
    	Scanner sc=new Scanner(System.in);
      	int t=sc.nextInt();
      	System.out.println(t*6.28318530717958623200);
    
    
    }

}
