import java.util.*;
class  Main
{
    public static void main (String[] args) 
    {
       Scanner sc =new Scanner(System.in); 
       System.out.println();
       int r=sc.nextInt();
       double c=0.0d;
       c=2*3.14*r;
       System.out.println(c);
       
    }
} import java.util.*; util.* java class  Main
{
    public static void main (String[] args) 
    {
       Scanner sc =new Scanner(System.in); 
       System.out.println();
       int r=sc.nextInt();
       double c=0.0d;
       c=2*3.14*r;
       System.out.println(c);
       
    }
} Main public static void main (String[] args) 
    {
       Scanner sc =new Scanner(System.in); 
       System.out.println();
       int r=sc.nextInt();
       double c=0.0d;
       c=2*3.14*r;
       System.out.println(c);
       
    } main {
       Scanner sc =new Scanner(System.in); 
       System.out.println();
       int r=sc.nextInt();
       double c=0.0d;
       c=2*3.14*r;
       System.out.println(c);
       
    } Scanner sc =new Scanner(System.in); sc new Scanner(System.in) System.out.println() System.out.println System.out System System.out int r=sc.nextInt(); r sc.nextInt() sc.nextInt sc double c=0.0d; c 0.0d c=2*3.14*r c 2*3.14*r 2*3.14*r 2 3.14 r System.out.println(c) System.out.println System.out System System.out c String[] args args
import java.util.*;
class  Main
{
    public static void main (String[] args) 
    {
       Scanner sc =new Scanner(System.in); 
       System.out.println();
       int r=sc.nextInt();
       double c=0.0d;
       c=2*3.14*r;
       System.out.println(c);
       
    }
}