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

[EX Q]: lrBJDRkT, jmBJDrI
[EX A]: BJD

[EX Q]: KfjqnJLciTXqkJK, yqfRcfqnJLcisSB
[EX A]: qnJLci

[EX Q]: IMrMaZmtbgdH, WfgrMaZmtbgRkRUl
[EX A]:
rMaZmtbg