import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    }
} Main public static void main(String[] args) {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    } main {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    } double pi = Math.PI; pi Math.PI Math Math.PI Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) double x = scanner.nextDouble(); x scanner.nextDouble() scanner.nextDouble scanner System.out.println(2 * pi * x) System.out.println System.out System System.out 2 * pi * x 2 * pi * x 2 pi x String[] args args public class Main {

    public static void main(String[] args) {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    }
} public class Main {

    public static void main(String[] args) {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        double pi = Math.PI;
        Scanner scanner = new Scanner(System.in);
        double x = scanner.nextDouble();
        //scanner.nextLine();
        System.out.println(2 * pi * x);
    }
}