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

Example Input: sdGIVJPsWWszKPCGk, ghRJPsWWszKcJUg
Example Output: JPsWWszK

Example Input: HaLZdTX, tLLZdEXN
Example Output: LZd

Example Input: pXSwcfMugXOA, mllcVGSwcfMugXmhZWyen
Example Output:
SwcfMugX