import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	}

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

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	}

} Main public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	} main {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	} Scanner scan=new Scanner(System.in); scan new Scanner(System.in) int R=scan.nextInt(); R scan.nextInt() scan.nextInt scan double d=Math.PI*(2*R); d Math.PI*(2*R) Math.PI Math Math.PI (2*R) 2 R System.out.println(d) System.out.println System.out System System.out d String[] args args public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	}

} public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scan=new Scanner(System.in);
		int R=scan.nextInt();
		double d=Math.PI*(2*R);
		System.out.println(d);
	}

}