import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    } main {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc System.out.println(2*r * 3.14) System.out.println System.out System System.out 2*r * 3.14 2*r * 3.14 2 r 3.14 String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        int r = sc.nextInt();
     
        System.out.println(2*r * 3.14);
    }
}
