import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  } main {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double n = sc.nextInt(); n sc.nextInt() sc.nextInt sc System.out.println(n * 2 * 3.14) System.out.println System.out System System.out n * 2 * 3.14 n * 2 * 3.14 n 2 3.14 sc.close() sc.close sc String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    double n = sc.nextInt();

    System.out.println(n * 2 * 3.14);
    sc.close();
  }
}
