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

Example Input: SQNzngllNbOkKDK, MijfNzngllNDfWge
Example Output: NzngllN

Example Input: gHFwDorPbNPORVgdLW, AfqDQvCGFwDorPbNPVPVmbQ
Example Output: FwDorPbNP

Example Input: UAwpcrfwh, KWipcrXtX
Example Output:
pcr