import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double c=2.0*(double)R*Math.PI;
		System.out.println(c);

	}

} 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 c=2.0*(double)R*Math.PI;
		System.out.println(c);

	}

} Main public static void main(String[] args) {
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double c=2.0*(double)R*Math.PI;
		System.out.println(c);

	} main {
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double c=2.0*(double)R*Math.PI;
		System.out.println(c);

	} Scanner scan=new Scanner(System.in); scan new Scanner(System.in) int R=scan.nextInt(); R scan.nextInt() scan.nextInt scan double c=2.0*(double)R*Math.PI; c 2.0*(double)R*Math.PI 2.0*(double)R*Math.PI 2.0 (double)R Math.PI Math Math.PI System.out.println(c) System.out.println System.out System System.out c String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double c=2.0*(double)R*Math.PI;
		System.out.println(c);

	}

} public class Main {

	public static void main(String[] args) {
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double c=2.0*(double)R*Math.PI;
		System.out.println(c);

	}

} 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 c=2.0*(double)R*Math.PI;
		System.out.println(c);

	}

}
