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

Example Input: QRPOwtZATjDoJDdRNNSOH, wiafFMwpAjDoJDdRNNuCDZ
Example Output: jDoJDdRNN

Example Input: hRVyvwHqnN, geHeyvwHqiBiYJ
Example Output: yvwHq

Example Input: VeCXCXdvbJsS, JLCXdvRRn
Example Output:
CXdv