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

Example Input: DFRoMPNDAzNgtLsEPseOzC, qykyPjDAzNgtLsEPYTsNrJaNK
Example Output: DAzNgtLsEP

Example Input: lkFGXvTkKm, wwELXvTkcOnG
Example Output: XvTk

Example Input: akyrmPcpkZleAEZpvWmjWQsW, EHrlkjWkZleAEZpvDgmgODBPI
Example Output:
kZleAEZpv