import java.util.Scanner;
public class Main {
   
    public static void main(String[] args) { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } 
} import java.util.Scanner; Scanner java.util public class Main {
   
    public static void main(String[] args) { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } 
} Main public static void main(String[] args) { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } main { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double R=sc.nextDouble(); R sc.nextDouble() sc.nextDouble sc System.out.printf("%.2f",2*3.14159*R) System.out.printf System.out System System.out "%.2f" 2*3.14159*R 2*3.14159*R 2 3.14159 R String[] args args public class Main {
   
    public static void main(String[] args) { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } 
} public class Main {
   
    public static void main(String[] args) { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } 
} Main
import java.util.Scanner;
public class Main {
   
    public static void main(String[] args) { 
		Scanner sc = new Scanner(System.in);
double R=sc.nextDouble();
        System.out.printf("%.2f",2*3.14159*R);
    } 
}