Hello all,.. need help with this one :

Given the series

$\displaystyle S = 1 - \frac{1}{\sqrt{2}} + \frac{1}{\sqrt{3}} - \frac{1}{\sqrt{4}} + \cdots$

If $\displaystyle S_n$ denote the partial sum of the first n term of this series, determine n such that the difference between $\displaystyle S$ and $\displaystyle S_n$ is less than 0.001.

any idea?

thx a lot.