import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    }

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

    public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    }

} Main public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    } main {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    } @SuppressWarnings("resource")
        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 * Math.PI) System.out.println System.out System System.out 2 * r * Math.PI 2 * r * Math.PI 2 r Math.PI Math Math.PI String[] args args public class Main {

    public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    }

} public class Main {

    public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    }

} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.println(2 * r * Math.PI);
    }

}
