import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    }
    } import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    }
    } Main public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    } main {
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int r = Integer.parseInt(scan.nextLine()); r Integer.parseInt(scan.nextLine()) Integer.parseInt Integer scan.nextLine() scan.nextLine scan System.out.println(2 * r * 3.14) System.out.println System.out System System.out 2 * r * 3.14 2 * r * 3.14 2 r 3.14 String[] args args public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    }
    } public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    }
    } Main
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = Integer.parseInt(scan.nextLine());
    System.out.println(2 * r * 3.14);
    }
    }