import java.util.Scanner;
public class Main
{
    public static void main(String Args[])
    {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    }
} import java.util.Scanner; Scanner java.util public class Main
{
    public static void main(String Args[])
    {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    }
} Main public static void main(String Args[])
    {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    } main {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    } Scanner sc=new Scanner (System.in); sc new Scanner (System.in) int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc double c=2*Math.PI*n; c 2*Math.PI*n 2*Math.PI*n 2 Math.PI Math Math.PI n System.out.println(c) System.out.println System.out System System.out c String Args[] Args public class Main
{
    public static void main(String Args[])
    {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    }
} public class Main
{
    public static void main(String Args[])
    {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    }
} Main
import java.util.Scanner;
public class Main
{
    public static void main(String Args[])
    {
        Scanner sc=new Scanner (System.in);
        int n=sc.nextInt();
        double c=2*Math.PI*n;
        System.out.println(c);
    }
}