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