/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
	Scanner s = new Scanner(System.in);
		while(s.hasNextLine()) {
			double r = s.nextInt();
			double d = s.nextInt();
			double r2 = (r*r)-((d*d)/4);
			double s2 = Math.PI*r2;	
			System.out.format(Locale.US, "%.2f%n",s2);
		}
	}
 
}
 

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MTAgMTAKMTAwMCAxNTAw

10 10
1000 1500