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); } }