import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		double c = sc.nextInt();
		double a = sc.nextInt();
		double b = sc.nextInt();
		double ans = Math.PI * Math.PI * (a + b) * (b - a) * (b - a) / 4.0 * c;
		System.out.println(ans);
   }
}