import java.util.Scanner;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  }
} 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 pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  } main {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double pi = 3.141592653558209749448214808651; pi 3.141592653558209749448214808651 double l = 2*pi*R; l 2*pi*R 2*pi*R 2 pi R System.out.println(l) System.out.println System.out System System.out l String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int R = sc.nextInt();
    double pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  }
} 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 pi = 3.141592653558209749448214808651;
    double l = 2*pi*R;
    System.out.println(l);
  }
}