Mahalanobis distance between two normal populations

The Mahalanobis distance between the two bivariate normal populations $N_2\!\left(\begin{pmatrix}1\\-1\end{pmatrix}, \begin{pmatrix}1&1\\1&4\end{pmatrix}\right)$ and $N_2\!\left(\begin{pmatrix}2\\-2\end{pmatrix}, \begin{pmatrix}1&1\\1&4\end{pmatrix}\right)$ is: