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

Example Input: ARGchkRez, kUwchkZPE
Example Output: chk

Example Input: kyADtWLlnmYv, tcaKvDtWLlnvBq
Example Output: DtWLln

Example Input: uHPTjmbVRITA, QavjmbVdPFM
Example Output:
jmbV