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

[EX Q]: EyvnjbVLF, vqnjblzR
[EX A]: njb

[EX Q]: UovaYpHjYSQzrfsxRfvIZE, pUOFxIKOGQzrfsxRfvIjrza
[EX A]: QzrfsxRfvI

[EX Q]: dgCekclCLM, gIQGekclUK
[EX A]:
ekcl