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: XbjDHRCWxdPbhibUKn, SrpuPDHRCWxdPbKPWEXNWbZ
Example Output: DHRCWxdPb

Example Input: QgTBuZzcYlspAzXshAtKQw, hAKHrcYlspAzXshKjXltQFpp
Example Output:
cYlspAzXsh