In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

Example Input: CxosNa, ikosdx
Example Output: os

Example Input: STvKOHq, XMGvKOdyM
Example Output: vKO

Example Input: nTDNIDzUmXBgUSeAjBYRNK, WCCUyoRZlzUmXBgUSeAbvwJkHFit
Example Output:
zUmXBgUSeA