import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	}
} Main public static void main(String[] args) {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	} main {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	} Scanner a = new Scanner(System.in); a new Scanner(System.in) int R = a.nextInt(); R a.nextInt() a.nextInt a double R2 = (R * 2) * 3.14; R2 (R * 2) * 3.14 (R * 2) R 2 3.14 System.out.println(R2) System.out.println System.out System System.out R2 String[] args args public class Main {

	public static void main(String[] args) {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	}
} public class Main {

	public static void main(String[] args) {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner a = new Scanner(System.in);		
		int R = a.nextInt();
		double R2 = (R * 2) * 3.14;
		System.out.println(R2);
	}
}