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]: QlJnxO, BLJnCQ
[EX A]: Jn

[EX Q]: uzccBSccDVpzDmiJrPnx, xllYQuoDVpzDmiJrTGDiyjov
[EX A]:
DVpzDmiJr