import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    }
} Main public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    } main {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    } Scanner input = new Scanner(System.in); input new Scanner(System.in) Integer R = input.nextInt(); R input.nextInt() input.nextInt input System.out.println(2 * Math.PI * R) System.out.println System.out System System.out 2 * Math.PI * R 2 * Math.PI * R 2 Math.PI Math Math.PI R String[] args args public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Integer R = input.nextInt();

        System.out.println(2 * Math.PI * R);
    }
}
