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

[EX Q]: HLtkkRnWkgIdqbQH, dWeFUtkkRnWkgIdZhlQh
[EX A]: tkkRnWkgId

[EX Q]: CxwZWv, mkwZgM
[EX A]: wZ

[EX Q]: MhwTcTdcepHV, yBVZUdwTcTdcepjkxvaV
[EX A]:
wTcTdcep