import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	}

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

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	} main {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc double circumference = r * 2 * Math.PI; circumference r * 2 * Math.PI r * 2 * Math.PI r 2 Math.PI Math Math.PI System.out.println(circumference) System.out.println System.out System System.out circumference String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int r = sc.nextInt();
		
		double circumference = r * 2 * Math.PI;
		
		System.out.println(circumference);
		
	}

}