import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    }
} Main public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    } main {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double r = Double.parseDouble(sc.next()); r Double.parseDouble(sc.next()) Double.parseDouble Double sc.next() sc.next sc System.out.println(r*2*Math.PI) System.out.println System.out System System.out r*2*Math.PI r*2*Math.PI r 2 Math.PI Math Math.PI String[] args args public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    }
} public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        double r = Double.parseDouble(sc.next());
        
        System.out.println(r*2*Math.PI);
    }
}