import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double a = sc.nextDouble();
		double b = sc.nextDouble();
		System.out.println(2 * Math.PI * (b - a));
	}

	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
}