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: PQCjJwXurLeN, vsjJwXuOy
Example Output: jJwXu

Example Input: KvWGeHBdj, ArBCWGeHXnp
Example Output:
WGeH