Complexity! (4)

Calculus Level 3

Let complex numbers $$z_{r}$$ be the roots of the polynomial $$\displaystyle \sum_{r=0}^{50} z^r$$ and that

$\displaystyle \left| \sum_{r=1}^{50} {\dfrac{1}{z_{r}-1}} \right| = a^{2}$

Find $$a$$, which is a positive integer.