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

[EX Q]: fdinRdwwlntwqzYGhV, ZefonRdwwlntoWQbh
[EX A]: nRdwwlnt

[EX Q]: IGHhMfqLeBpnullsPInfBH, LTDBpnullsPIBynwCrCQ
[EX A]: BpnullsPI

[EX Q]: ilQSYHZRTQsNyhP, VrjYHZRTQsNMQH
[EX A]:
YHZRTQsN