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

Example Input: YKpdeJQhzyYiPoODACUu, mjmnIlCehzyYiPoOzZ
Example Output: hzyYiPoO

Example Input: hRVyvwHqnN, geHeyvwHqiBiYJ
Example Output: yvwHq

Example Input: LKtIeRESPtAZgct, nwPprVXtIeRESPtAQNCBfow
Example Output:
tIeRESPtA