import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) {
		BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));

		try {
			int cal = Integer.parseInt(buff.readLine());
			String[] box = buff.readLine().split(" ");

			int in = Integer.parseInt(box[0]);
			int out = Integer.parseInt(box[1]);

			double ans = 0d;

			double outer = (out - in) / 2.0d;
			double inner = (in + outer);
			double area = outer * outer * Math.PI * inner * 2 * Math.PI;

			ans = area * cal;

			System.out.println(ans);
		} catch (NumberFormatException e) {
			e.getStackTrace();
		} catch (IOException e) {
			e.getStackTrace();
		} catch (Exception e) {
			e.getStackTrace();
		}
	}
}