import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	}

} 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();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	}

} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	} main {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int r = scan.nextInt(); r scan.nextInt() scan.nextInt scan double ans = 0; ans 0 ans = 2 * Math.PI * r ans 2 * Math.PI * r 2 * Math.PI * r 2 Math.PI Math Math.PI r System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	}

} public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	}

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

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int r = scan.nextInt();
		double ans = 0;
		
		ans = 2 * Math.PI * r;
		System.out.println(ans);

	}

}