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

[EX Q]: FiKGCRXutEOzMqP, xdxRXutEsl
[EX A]: RXutE

[EX Q]: YKpdeJQhzyYiPoODACUu, mjmnIlCehzyYiPoOzZ
[EX A]: hzyYiPoO

[EX Q]: snBULlDv, gaULlxmL
[EX A]:
ULl