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

Example Input: yxJxNRLEnKGHziJtfb, KfReWhEnKGHzitzfPWzK
Example Output: EnKGHzi

Example Input: srPyjmTQhdFFMcQ, QQGBdtyjmTQhmfEy
Example Output: yjmTQh

Example Input: ryRRhuYCwXbnMJaWC, vqFpGYCwXbnLii
Example Output:
YCwXbn