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

Example Input: RNYHvcNnbsUdJLvS, PpNnbsUdglWhl
Example Output: NnbsUd

Example Input: lQwpMQRxuVbJDv, UkzwpMQRxuDVT
Example Output: wpMQRxu

Example Input: whbKlalyJpdlmkJIw, sGlalyJpdlPste
Example Output:
lalyJpdl