import java.util.Scanner;

public class  Main {
	public static void main(String[] args) {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	}
} import java.util.Scanner; Scanner java.util public class  Main {
	public static void main(String[] args) {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	}
} Main public static void main(String[] args) {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	} main {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	} double r; r double area; area Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) r = scanner.nextDouble() r scanner.nextDouble() scanner.nextDouble scanner area = r * 3.14 * 2 area r * 3.14 * 2 r * 3.14 * 2 r 3.14 2 System.out.println(area) System.out.println System.out System System.out area String[] args args public class  Main {
	public static void main(String[] args) {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	}
} public class  Main {
	public static void main(String[] args) {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	}
} Main
import java.util.Scanner;

public class  Main {
	public static void main(String[] args) {
		double r;
		double area;
		Scanner scanner = new Scanner(System.in);
		
		r = scanner.nextDouble();
		
		area = r * 3.14 * 2;
		
		System.out.println(area);
	}
}