import java.io.*;

class Main{
	public static void main(String[] args){
      
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in) );
  	try{
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       }catch(Exception e){
 	   }
   }
} import java.io.*; io.* java class Main{
	public static void main(String[] args){
      
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in) );
  	try{
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       }catch(Exception e){
 	   }
   }
} Main public static void main(String[] args){
      
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in) );
  	try{
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       }catch(Exception e){
 	   }
   } main {
      
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in) );
  	try{
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       }catch(Exception e){
 	   }
   } BufferedReader br = new BufferedReader(new InputStreamReader(System.in) ); br new BufferedReader(new InputStreamReader(System.in) ) try{
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       }catch(Exception e){
 	   } catch(Exception e){
 	   } Exception e {
 	   } {
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       } String str = br.readLine(); str br.readLine() br.readLine br int num = Integer.parseInt(str); num Integer.parseInt(str) Integer.parseInt Integer str double p = 3.14; p 3.14 System.out.println(2.0*p*num) System.out.println System.out System System.out 2.0*p*num 2.0*p*num 2.0 p num String[] args args
import java.io.*;

class Main{
	public static void main(String[] args){
      
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in) );
  	try{
  			String str = br.readLine();
  			int num = Integer.parseInt(str);
  
  			double p = 3.14;
  
  			System.out.println(2.0*p*num);
       }catch(Exception e){
 	   }
   }
}