Covariance of buying coffee and buying a pastry

Let $X = 1$ if a customer buys coffee (else $0$) and $Y = 1$ if they buy a pastry (else $0$). The shop's data gives the joint chances of each combination:

	$Y=0$	$Y=1$
$X=0$	0.40	0.10
$X=1$	0.20	0.30

What is the covariance of $X$ and $Y$?