import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	}
} Main public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	} main {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int r = Integer.parseInt(scanner.nextLine()); r Integer.parseInt(scanner.nextLine()) Integer.parseInt Integer scanner.nextLine() scanner.nextLine scanner System.out.println(r * 6.28318530717958623200d) System.out.println System.out System System.out r * 6.28318530717958623200d r 6.28318530717958623200d String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int r = Integer.parseInt(scanner.nextLine());
		System.out.println(r * 6.28318530717958623200d);
	}
}
