import java.util.Scanner;
public class Main{
public static void main(String[]args){

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

}
} import java.util.Scanner; Scanner java.util public class Main{
public static void main(String[]args){

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

}
} Main public static void main(String[]args){

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

} main {

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

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

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

}
} public class Main{
public static void main(String[]args){

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

}
} Main
import java.util.Scanner;
public class Main{
public static void main(String[]args){

Scanner sc=new Scanner(System.in);

int R =sc.nextInt();
double ans=R*6.28318530717958623200;
  System.out.println(ans);

}
}