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

[EX Q]: XqyPjqNZDEK, EfwPjqNgjIP
[EX A]: PjqN

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

[EX Q]: WVYqwO, khYqBB
[EX A]:
Yq