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