Question 4
Bruno chooses a positive integer $X$. Then Flor chooses four integers $a, b, c, d$ and computes $N = (a-b)(b-c)(c-d)(d-a)(a-c)(b-d)$, the product of the six differences between these four numbers. Determine the largest value of $X$ for which Bruno can be certain that $N$ will be a multiple of $X$.