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

Example Input: oDdulHNcCdgbRGxiBTxM, kDcCdgbRGnsJlvas
Example Output: cCdgbRG

Example Input: yKtQOhYvrJVH, HQsTQOhYvPP
Example Output: QOhYv

Example Input: kLMqkNCHk, QqWMqkNCJUp
Example Output:
MqkNC