t = linspace(0, 2*pi, 100);
cla reset; hold on
for r = 21:-1:2
	if mod(r,2)
		fill(r*cos(t), r*sin(t), 'k')
	else
		fill(r*cos(t), r*sin(t), 'w')
	end
end
fill(cos(t), sin(t), 'r')
axis equal; hold off
