import java.util.Scanner;

public class Main {

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

} import java.util.Scanner; Scanner java.util public class Main {

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

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

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

} public class Main {

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

} Main
import java.util.Scanner;

public class Main {

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

}
