import java.util.Scanner;

/*
 * @author Tanzim Ibn Patowary
 * Created  Apr 25, 2020 3:55:23 AM
 */
public class Main {

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

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

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

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

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

} public class Main {

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

} Main
import java.util.Scanner;

/*
 * @author Tanzim Ibn Patowary
 * Created  Apr 25, 2020 3:55:23 AM
 */
public class Main {

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

}
