import java.util.Scanner;
import java.lang.Math;

public class Main {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int R = scan.nextInt();
    scan.close();

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

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

    System.out.println(2*Math.PI*R);
  } main {
    Scanner scan = new Scanner(System.in);
    int R = scan.nextInt();
    scan.close();

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

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

    System.out.println(2*Math.PI*R);
  }
} Main
import java.util.Scanner;
import java.lang.Math;

public class Main {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int R = scan.nextInt();
    scan.close();

    System.out.println(2*Math.PI*R);
  }
}