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

Example Input: UiaECWZf, gRyaECWLGRl
Example Output: aECW

Example Input: HhBhJMpxpty, MxTJMpxnQEf
Example Output: JMpx

Example Input: xKywNbWkhBOzPINOTtpk, sChBOzPINOKJ
Example Output:
hBOzPINO