import java.util.Scanner;
public class No89 {
	public static void main(String[] args){
		Scanner sc =new Scanner(System.in);
		int c=sc.nextInt();
		double in=sc.nextDouble();
		double out=sc.nextDouble();
		System.out.println(c*Math.PI*Math.PI/4*(in+out)*(in-out)*(in-out));
	}
}