Infinite Sequences and Series · Easy problem

A signal-processing algorithm's worst-case cumulative error is bounded by $\displaystyle\sum_{n=1}^{\infty}\dfrac{c}{n^2}=\dfrac{c\pi^2}6$ (using $\displaystyle\sum_{n=1}^{\infty}\dfrac1{n^2}=\dfrac{\pi^2}6$), for a positive integer constant $c$. Engineers require this worst-case bound to be no more than $5$ units. What is the largest value of $c$ they can use?