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

Example Input: sGrHRmELarByxp, cDCUnmELarBXbEfM
Example Output: mELarB

Example Input: YCAyruPTTHWhCYaiXfIl, OETdzqAyruPTTHWgS
Example Output: AyruPTTHW

Example Input: gzzaAbn, oLzaAvn
Example Output:
zaA