import java.util.Scanner;

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

                double R = scan.nextDouble();
                scan.close();

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

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

                double R = scan.nextDouble();
                scan.close();

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

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

                double R = scan.nextDouble();
                scan.close();

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

                double R = scan.nextDouble();
                scan.close();

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

                double R = scan.nextDouble();
                scan.close();

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

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

                double R = scan.nextDouble();
                scan.close();

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

} Main
import java.util.Scanner;

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

                double R = scan.nextDouble();
                scan.close();

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

}