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

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

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

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

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

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

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

        } main {
                Scanner scan = new Scanner(System.in);
                String str = scan.nextLine();

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

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

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

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

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

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

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

                System.out.println(Integer.parseInt(str) * 2 * Math.PI);
                scan.close();

        }
}
