If $z$ and $\omega$ are two complex numbers such that $|z\omega| = 1$ and $\arg(z) - \arg(\omega) = 3\pi/2$, then $\arg\left(\frac{1 - 2z\omega}{1 + 3z\omega}\right)$ is: (Here $\arg(z)$ denotes the principal argument of complex number $z$)