import java.util.Scanner;

public class Main {
    public static void main(String... args) {
        Scanner scanner = new Scanner(System.in);

        double R = (double) scanner.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 scanner = new Scanner(System.in);

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

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

        double R = (double) scanner.nextInt();
        System.out.println(2 * Math.PI * R);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) double R = (double) scanner.nextInt(); R (double) scanner.nextInt() scanner.nextInt scanner 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 scanner = new Scanner(System.in);

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

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

public class Main {
    public static void main(String... args) {
        Scanner scanner = new Scanner(System.in);

        double R = (double) scanner.nextInt();
        System.out.println(2 * Math.PI * R);
    }
}
