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

Example Input: ZRjPgqbLL, uIsmPgqbBB
Example Output: Pgqb

Example Input: ilgSzrcUKLTNLJbMKMKSt, hFXIuUKLTNLJbMKWxSCkDjY
Example Output: UKLTNLJbMK

Example Input: CqkPcMZsDdAeoKBhR, OdeVvqZsDdAeoKBOlJkfStPm
Example Output:
ZsDdAeoKB