$p=atan2 1,0;
($a,$b)=<>;
if($a>=0){
	print 4*$p*((1-$a)**2-(1-$b)**2)
}elsif($b<=0){
	print 4*$p*((1+$a)**2-(1+$b)**2)
}else{
	print 4*$p*(1-(1+$a)**2+1-(1-$b)**2)
}