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

Example Input: BrDGrTD, PBHDGrDw
Example Output: DGr

Example Input: LeHzcEFc, WFzcExvJ
Example Output: zcE

Example Input: jwPoCValsOXiwIJZKwPTx, EMeOlIEjOXiwIJZKwPqHgd
Example Output:
OXiwIJZKwP