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