Tail probability of a linear combination of correlated standard normals

Let $\underline X=(X_1,X_2)$ have a bivariate normal distribution with $E(X_1)=E(X_2)=0$, $E(X_1^2)=E(X_2^2)=1$ and $E(X_1X_2)=\frac12$. Then $P\left(X_1+2X_2>\sqrt7\right)=$