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

[EX Q]: tmBlKUto, eFDBlKLy
[EX A]: BlK

[EX Q]: wYhGWdRC, cFGWdHEy
[EX A]: GWd

[EX Q]: dXYuYKanqHrsaglPsUwXzTyAeOCd, OKwrsaglPsUwXksf
[EX A]:
rsaglPsUwX