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

Example Input: krnkpodgfpCKtfCqyzUbymWbxi, DydgSWpCKtfCqyzDaMsjqc
Example Output: pCKtfCqyz

Example Input: oGaGjsaKsUpLQAg, iDGjsaKsUoYGuta
Example Output: GjsaKsU

Example Input: TzRAlkoWPwpMlhcBiaDL, hXRAlkoWPwptp
Example Output:
RAlkoWPwp