import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    } main {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) double r = scanner.nextDouble(); r scanner.nextDouble() scanner.nextDouble scanner System.out.println(r * 2 * 3.14) System.out.println System.out System System.out r * 2 * 3.14 r * 2 * 3.14 r 2 3.14 String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double r = scanner.nextDouble();
        System.out.println(r * 2 * 3.14);
    }
}
