import java.util.Scanner;
public class Main {

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

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

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

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

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		double l = s.nextDouble();
		System.out.println(l * 2 * 3.14);
		s.close();
	}
}
