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

[EX Q]: RtOkkgLvhgfGlX, vCOkgLvhzOa
[EX A]: kgLvh

[EX Q]: iaXeqfIrYKxPJRXxfSm, rIYKxPJRXxfsjVsqe
[EX A]: YKxPJRXxf

[EX Q]: oDPNTubuSHyMR, cPIdubuSHeBC
[EX A]:
ubuSH