import java.util.Scanner;

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

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