import java.util.*;

public class Main {

	public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
}

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

	public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
}

} Main public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
} main {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
} Scanner s = new Scanner(System.in); s new Scanner(System.in) int r = s.nextInt(); r s.nextInt() s.nextInt s double ans = 0.11f; ans 0.11f ans = 2 * 3.14 * r ans 2 * 3.14 * r 2 * 3.14 * r 2 3.14 r System.out.printf("%.2f", ans) System.out.printf System.out System System.out "%.2f" ans String[] args args public class Main {

	public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
}

} public class Main {

	public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
}

} Main
import java.util.*;

public class Main {

	public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int r = s.nextInt();
		double ans = 0.11f;
		ans = 2 * 3.14 * r;
		System.out.printf("%.2f", ans);
}

}
