import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
public class Main {
 
	
    public static double round(double val, int places) {
        long factor = (long)Math.pow(10,places);
        val = val * factor;
        long tmp = Math.round(val);
       return (double)tmp / factor;
    }
    
	public static void main(String[] args) {
 
		double Pi=3.141592654;
		double r=0.00,d=0.00,wyn=0.00,a=0.00,b=0.00,h_kwadrat=0.00;
 
		BufferedReader stdin = new BufferedReader( new InputStreamReader(System.in));
		try {
			String[] linia = stdin.readLine().split(" ");
			double rDouble  = Double.parseDouble(linia[0]);
			r=rDouble;
			double dDouble =  Double.parseDouble(linia[1]);
			d=dDouble;
		} catch (Exception e) {
			System.exit(1);
		}
 
 
	      b=r;
	      a=d/2;
	      h_kwadrat=(b*b) - (a*a);
	      wyn = h_kwadrat*Pi;
	      wyn = round(wyn, 2);
	      
	      System.out.println(wyn);
 
	}
}