import java.util.Scanner;

public class Main {

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

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

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

public class Main {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int r = sc.nextInt();
    System.out.println(r * 2 * Math.PI);
  }
}