Conditional variance in a trivariate normal

Let $(X_1, X_2, X_3)^T$ follow a trivariate normal distribution with mean vector $\mu$ and covariance matrix $\Sigma$ given by $\mu = (1, 1, 1)^T$ and $\Sigma = \begin{pmatrix} 2 & 1 & 1 \ 1 & 2 & 1 \ 1 & 1 & 2 \end{pmatrix}$. Then $\operatorname{Var}(X_1 | X_2 = 1, X_3 = -1)$ equals ________ (rounded off to two decimal places).