A protein is to be purified using ion-exchange column chromatography. The relationship between HETP (Height Equivalent to Theoretical Plate) and the linear liquid velocity of mobile phase is given by:

$H = \dfrac{A}{u} + Bu + C$

Where $H$ is HETP (m) and $u$ is linear liquid velocity of mobile phase $(ms^{-1})$. The values of $A, B$ and $C$ are $3 \times 10^8 \: m^2 \cdot s^{-1}$, $3 \: s$ and $6 \times 10^{-5} m$, respectively. The number of theoretical plates based on minimum HETP for a column of $66$ cm length will be _________