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

Example Input: IQIHqbEhpVuNATp, GIJIHqbEhpzWb
Example Output: IHqbEhp

Example Input: HSsyZzZLZAAq, MFEZzZLJC
Example Output: ZzZL

Example Input: tVJuYFkjnctcwvy, NnjkFkjnctZtDn
Example Output:
Fkjnct