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

Example Input: WFAPUCgVYbmZiFlacUzyv, xQFiekrgPUCgVYbmZUEtl
Example Output: PUCgVYbmZ

Example Input: UldKHMpUYADGfEUGcSon, nPHMpUYADGfEKqHCLPmL
Example Output: HMpUYADGfE

Example Input: JkBWFAwckGgv, UAwnWFAwceLCNO
Example Output:
WFAwc