import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	} main {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double R = (double) sc.nextInt(); R (double) sc.nextInt() sc.nextInt sc System.out.println(R * 2 * 3.1415) System.out.println System.out System System.out R * 2 * 3.1415 R * 2 * 3.1415 R 2 3.1415 String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = (double) sc.nextInt();
		System.out.println(R * 2 * 3.1415);
	}
}