import java.util.Scanner;

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

    int r = sc.nextInt();
    double ret = r * 2 * 3.14159;
    System.out.println(ret);
  }
} 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 ret = r * 2 * 3.14159;
    System.out.println(ret);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();
    double ret = r * 2 * 3.14159;
    System.out.println(ret);
  } main {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();
    double ret = r * 2 * 3.14159;
    System.out.println(ret);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc double ret = r * 2 * 3.14159; ret r * 2 * 3.14159 r * 2 * 3.14159 r 2 3.14159 System.out.println(ret) System.out.println System.out System System.out ret String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();
    double ret = r * 2 * 3.14159;
    System.out.println(ret);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();
    double ret = r * 2 * 3.14159;
    System.out.println(ret);
  }
} 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 ret = r * 2 * 3.14159;
    System.out.println(ret);
  }
}
