import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    }
} Main public static void main(String[] args) {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    } main {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    } int R; R Scanner scan = new Scanner(System.in); scan new Scanner(System.in) R=scan.nextInt() R scan.nextInt() scan.nextInt scan double L; L L=R*2*3.14 L R*2*3.14 R*2*3.14 R 2 3.14 System.out.println(L) System.out.println System.out System System.out L String[] args args public class Main {

    public static void main(String[] args) {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    }
} public class Main {

    public static void main(String[] args) {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
	// write your code here


        int R;
       


Scanner scan = new Scanner(System.in);
 R=scan.nextInt();



        double L;
        L=R*2*3.14;
        System.out.println(L);




    }
}
