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

Example Input: MvALRGKkpALcKdhTtnm, neMkRGKkpALcKdcaxnXEPxW
Example Output: RGKkpALcKd

Example Input: bjjsMtBzzXIgYWPBZmaDL, iTxktmvBzzXIgYWPhbAyBE
Example Output: BzzXIgYWP

Example Input: BUFfKHpNs, sgfKHPA
Example Output:
fKH