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

Example Input: AxRSlkQfWHrdlgQG, iXIOrmlkQfWHTy
Example Output: lkQfWH

Example Input: ohueEOjHvAuoFVmMFft, ovdJPqOjHvAuoFVGbvxzlnE
Example Output: OjHvAuoFV

Example Input: PGczsHbVfThPxJQ, mbeSRsHbVfThzIagY
Example Output:
sHbVfTh