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

Example Input: bdCOjNchdKtvWzOI, FwejNchdKhEd
Example Output: jNchdK

Example Input: XjYkMfARxWBSBjuXyDrFt, EtUxIfiHkMfARxWBSckTLTTnR
Example Output: kMfARxWBS

Example Input: bFpNfC, pzpNNZ
Example Output:
pN

