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

[EX Q]: UiaECWZf, gRyaECWLGRl
[EX A]: aECW

[EX Q]: ztkWLUJQXxP, fYluOkWLUJKDX
[EX A]: kWLUJ

[EX Q]: DYysQsvpYFLBQQIxsVdn, MPwQsvpYFLBQQNGMRlld
[EX A]:
QsvpYFLBQQ