public class Main{
 public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 }
} public class Main{
 public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 }
} Main public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 } main {
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 } int R = new java.util.Scanner ( System.in ).nextInt (); R new java.util.Scanner ( System.in ).nextInt () new java.util.Scanner ( System.in ).nextInt new java.util.Scanner ( System.in ) double enshu = 2 * Math.PI * R; enshu 2 * Math.PI * R 2 * Math.PI * R 2 Math.PI Math Math.PI R System.out.println(enshu) System.out.println System.out System System.out enshu String[] args args public class Main{
 public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 }
} public class Main{
 public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 }
} Main
public class Main{
 public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 }
}