import java.util.Scanner;

public class Main
{
    public  static  void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    }
} import java.util.Scanner; Scanner java.util public class Main
{
    public  static  void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    }
} Main public  static  void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    } main {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double a = sc.nextDouble(); a sc.nextDouble() sc.nextDouble sc a = a*2*3.14159 a a*2*3.14159 a*2*3.14159 a 2 3.14159 System.out.print((a)) System.out.print System.out System System.out (a) String[] args args public class Main
{
    public  static  void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    }
} public class Main
{
    public  static  void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    }
} Main
import java.util.Scanner;

public class Main
{
    public  static  void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        a = a*2*3.14159;
        System.out.print((a));

    }
}
