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

Example Input: rPPfxUdowLLdvwRtY, PuHovApkfxUdowLLBOhq
Example Output: fxUdowLL

Example Input: kvutZfcPKzHE, kTKutZfcPTGmU
Example Output: utZfcP

Example Input: UldKHMpUYADGfEUGcSon, nPHMpUYADGfEKqHCLPmL
Example Output:
HMpUYADGfE