AIME 2019a Problem 10

For distinct complex numbers $z_1,z_2,\dots,z_{673}$, the polynomial $$(x-z_1)^3(x-z_2)^3 \cdots (x-z_{673})^3$$can be expressed as $x^{2019} + 20x^{2018} + 19x^{2017}+g(x)$, where $g(x)$ is a polynomial with complex coefficients and with degree at most $2016$. The sum $$\left| \sum_{1 \le j <k \le 673} z_jz_k \right|$$ can be expressed in the form $\frac{m}{n}$, where $m$ and $n$ are relatively prime positive integers. Find $m+n$.