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

Example Input: EOacPYivmmUlYenynBqAwx, MoZWMOeXmUlYenynBEendWg
Example Output: mUlYenynB

Example Input: BeEgLISxThm, UGLISxEtP
Example Output: LISx

Example Input: pttGyitYvYVidvJmmtBgNRG, kFHhcRtbxYvYVidvJmmVIrIl
Example Output:
YvYVidvJmm