Let $X$ and $Y$ be discrete random variables with $P(X=1, Y=1) = 0.1$, $P(X=1, Y=0) = 0.2$, $P(X=0, Y=1) = 0.3$, and $P(X=0, Y=0) = 0.4$. What is the covariance $Cov(X, Y)$?