import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	}
} Main public static void main(String[] args) {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	} main {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	} Scanner kbs = new Scanner(System.in); kbs new Scanner(System.in) int r = kbs.nextInt(); r kbs.nextInt() kbs.nextInt kbs double s = 0; s 0 s = 2 * 3.14 * r s 2 * 3.14 * r 2 * 3.14 * r 2 3.14 r System.out.println(s) System.out.println System.out System System.out s String[] args args public class Main {
	public static void main(String[] args) {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	}
} Main
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner kbs = new Scanner(System.in);
		int r = kbs.nextInt();
		double s = 0;
		s = 2 * 3.14 * r;
		System.out.println(s);
	}
}