
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	}
} Main public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	} main {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) double a  = scanner.nextInt(); a scanner.nextInt() scanner.nextInt scanner double c = 3.141592653589793238; c 3.141592653589793238 double b = 2 * c * a; b 2 * c * a 2 * c * a 2 c a System.out.println(b) System.out.println System.out System System.out b String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	}
} public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	}
} Main

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		double a  = scanner.nextInt();
		double c = 3.141592653589793238;
		double b = 2 * c * a;
		System.out.println(b);
	}
}