import java.util.*;
import java.io.*;
public class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  }
}  import java.util.*; util.* java import java.io.*; io.* java public class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  }
} Main public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  } main {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) double pi=3.14159265; pi 3.14159265 double rad; rad rad=sc.nextDouble() rad sc.nextDouble() sc.nextDouble sc double cir; cir cir=2*pi*rad cir 2*pi*rad 2*pi*rad 2 pi rad System.out.printf("%.2f" ,cir) System.out.printf System.out System System.out "%.2f" cir String args[] args public class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  }
} public class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  }
} Main
import java.util.*;
import java.io.*;
public class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    double pi=3.14159265;
    double rad;
    rad=sc.nextDouble();
    double cir;
    cir=2*pi*rad;
    System.out.printf("%.2f" ,cir);
  }
} 