import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    String str = scan.nextLine();
    double res = Integer.parseInt(str);
    res = res * 2 * Math.PI;
    System.out.println(res);
  }

} import java.util.Scanner; Scanner java.util class Main {
  public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    String str = scan.nextLine();
    double res = Integer.parseInt(str);
    res = res * 2 * Math.PI;
    System.out.println(res);
  }

} Main public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    String str = scan.nextLine();
    double res = Integer.parseInt(str);
    res = res * 2 * Math.PI;
    System.out.println(res);
  } main {

    Scanner scan = new Scanner(System.in);
    String str = scan.nextLine();
    double res = Integer.parseInt(str);
    res = res * 2 * Math.PI;
    System.out.println(res);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String str = scan.nextLine(); str scan.nextLine() scan.nextLine scan double res = Integer.parseInt(str); res Integer.parseInt(str) Integer.parseInt Integer str res = res * 2 * Math.PI res res * 2 * Math.PI res * 2 * Math.PI res 2 Math.PI Math Math.PI System.out.println(res) System.out.println System.out System System.out res String[] args args
import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    String str = scan.nextLine();
    double res = Integer.parseInt(str);
    res = res * 2 * Math.PI;
    System.out.println(res);
  }

}
