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

Example Input: zeuyZKwvIOfx, BlmZKwvspUt
Example Output: ZKwv

Example Input: VByrCcgcxCfPGDFqIWGloQZTMQf, OqfPGDFqIWGlalTCCkKkMf
Example Output: fPGDFqIWGl

Example Input: iCOlSdAVXXX, ahlSdApBje
Example Output:
lSdA