An algebra problem by Dharani Chinta

Let $N$ be any four-digit integer $\overline{x_1x_2x_3x_4}$ , where $x_1$ , $x_2$ , $x_3$ , and $x_4$ are single-digit positive integers and $x_1 \ne 0$ .

Find the maximum value of $\left \lfloor \dfrac{N}{x_1 + x_2 + x_3 + x_4} \right \rfloor$ , where $\lfloor \cdot \rfloor$ denotes the floor function .