import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


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

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


	}
} Main public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


	} main {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int n = Integer.parseInt(scanner.nextLine()); n Integer.parseInt(scanner.nextLine()) Integer.parseInt Integer scanner.nextLine() scanner.nextLine scanner System.out.println(n * 2 * Math.PI) System.out.println System.out System System.out n * 2 * Math.PI n * 2 * Math.PI n 2 Math.PI Math Math.PI String[] args args public class Main {

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


	}
} public class Main {

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		int n = Integer.parseInt(scanner.nextLine());

		System.out.println(n * 2 * Math.PI);


	}
}
