import java.util.Scanner;

public class Main {

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

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	}

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

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

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	}

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

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	} main {
		Scanner scanner = new Scanner(System.in);

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int radius = scanner.nextInt(); radius scanner.nextInt() scanner.nextInt scanner double circle = radius * 2 * 3.14; circle radius * 2 * 3.14 radius * 2 * 3.14 radius 2 3.14 System.out.println(circle) System.out.println System.out System System.out circle scanner.close() scanner.close scanner String[] args args public class Main {

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

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	}

} public class Main {

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

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	}

} Main
import java.util.Scanner;

public class Main {

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

		int radius = scanner.nextInt();

		double circle = radius * 2 * 3.14;
		//double circle = radius * 2 * Math.PI;

		System.out.println(circle);

		scanner.close();
	}

}
