import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) throws Exception {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    }
} Main public static void main(String[] args) throws Exception {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    } main {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592) System.out.println System.out System System.out Integer.parseInt(scan.nextLine()) * 2 * 3.141592 Integer.parseInt(scan.nextLine()) * 2 * 3.141592 Integer.parseInt(scan.nextLine()) Integer.parseInt Integer scan.nextLine() scan.nextLine scan 2 3.141592 String[] args args public class Main {
    public static void main(String[] args) throws Exception {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    }
} public class Main {
    public static void main(String[] args) throws Exception {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {

        Scanner scan = new Scanner(System.in);
        System.out.println(Integer.parseInt(scan.nextLine()) * 2 * 3.141592);
        
    }
}