import java.util.Scanner;


public class Main {
	public static void main(String[] a) {
		Scanner s=new Scanner(System.in);
		int C=s.nextInt(),I=s.nextInt(),O=s.nextInt(),P=O+I,M=O-I;
		System.out.println(Math.PI*Math.PI*P*M*M*C/4);
	}
}