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

Example Input: PzXzvmYrlGZgOBk, iKnzvmYrlGZgOrs
Example Output: zvmYrlGZgO

Example Input: fdxgzAMP, xrcxgzYW
Example Output: xgz

Example Input: bNnwGtCYxQhNQiYapbXOC, RLwcTYxQhNQiTc
Example Output:
YxQhNQi