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

Example Input: fWJdaAfOCfejXZvidHM, gOpfOCfejXZbtLvSLZI
Example Output: fOCfejXZ

Example Input: GBTHKtWUzK, ovVNKtWUmVJF
Example Output: KtWU

Example Input: WVkcUyaFhhK, LzWkcUyaPlso
Example Output:
kcUya

