import java.util.Scanner;
public class No89 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		double c = s.nextDouble() , rin = s.nextDouble() , rout = s.nextDouble();
		s.close();

		double rhalf = rin + (rout - rin) / 2;
		System.out.println(c * Math.pow((rout-rin)/2,2) * 2 * rhalf * Math.pow(Math.PI,2));

	}

}