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

Example Input: jeQzwP, kSQzxq
Example Output: Qz

Example Input: plSfJAktMfac, TCjYJAktlt
Example Output: JAkt

Example Input: mGvfYCtHLolL, oxpsyfYCtHHjNG
Example Output:
fYCtH