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

Example Input: PGjDRPDzGaBR, rpIJRPDzWi
Example Output: RPDz

Example Input: SUueHhzGsanfsalEEc, KygEhzGsanfsapbKKX
Example Output: hzGsanfsa

Example Input: zeMbVsRMEo, sLQkbVsRDa
Example Output:
bVsR