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

[EX Q]: cUCQXEFSgRZjK, RYdvUQXEFSgRZVlwx
[EX A]: QXEFSgRZ

[EX Q]: kOrQWjLKnwN, xFsWjLKgr
[EX A]: WjLK

[EX Q]: RLSkBtbXFvgIMP, pxgBtbXFzu
[EX A]:
BtbXF