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

Example Input: KvPFobZEGs, eKFobZEtnm
Example Output: FobZE

Example Input: mJoHBJehHtkFS, ZMrDxHBJehHtxS
Example Output: HBJehHt

Example Input: XuWqQRWy, PDBWqQJUl
Example Output:
WqQ