import java.util.Scanner;

public class Yukicoder89 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double c = sc.nextDouble();
		double ri = sc.nextDouble(), ro = sc.nextDouble();

		double res = c * Math.PI * (ro - ri) * (ro - ri) * Math.PI  * (ro + ri) / 4.0;
		System.out.println(res);
	}
}