import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	}

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

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	}

} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	} main {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int R = scan.nextInt(); R scan.nextInt() scan.nextInt scan System.out.println(R*2*3.14) System.out.println System.out System System.out R*2*3.14 R*2*3.14 R 2 3.14 String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	}

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

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		
		System.out.println(R*2*3.14);
	}

}
