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

Example Input: BUvWkxrAvDQG, rHrkxrAkCE
Example Output: kxrA

Example Input: KKebLWQCQzVIojj, nxQCQzVIopD
Example Output: QCQzVIo

Example Input: IYoItBEfE, MDheoItBrJd
Example Output:
oItB