import java.util.Scanner;
public class Main
{
  public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  }
} import java.util.Scanner; Scanner java.util public class Main
{
  public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  }
} Main public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  } main {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double result = 2 * 3.141592653589793238 * R; result 2 * 3.141592653589793238 * R 2 * 3.141592653589793238 * R 2 3.141592653589793238 R System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main
{
  public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  }
} public class Main
{
  public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  }
} Main
import java.util.Scanner;
public class Main
{
  public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double result = 2 * 3.141592653589793238 * R;
    System.out.println(result);
  }
}
