import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		
		int R = scanner.nextInt();
		
		scanner.close();
		
		System.out.println(2 * R * 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 R = scanner.nextInt();
		
		scanner.close();
		
		System.out.println(2 * R * Math.PI);
	}

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

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		
		int R = scanner.nextInt();
		
		scanner.close();
		
		System.out.println(2 * R * Math.PI);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		
		int R = scanner.nextInt();
		
		scanner.close();
		
		System.out.println(2 * R * Math.PI);
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		
		int R = scanner.nextInt();
		
		scanner.close();
		
		System.out.println(2 * R * Math.PI);
	}

}
