Condition for differentiability at a point of a split rational irrational function

Let $f:\mathbb R\to\mathbb R$ be defined by

$$f(x)=\begin{cases}x^2, & \text{if }x\in\mathbb Q,\ \alpha x+\beta, & \text{if }x\in\mathbb R-\mathbb Q,\end{cases}$$

where $\alpha$ and $\beta$ are real constants. If $f$ is differentiable at $x=1$ then the value of $3\alpha+\beta$ is equal to ____________