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

Example Input: yKtQOhYvrJVH, HQsTQOhYvPP
Example Output: QOhYv

Example Input: fREVIdeTcakgFnwDWTVev, IbtXImseeTcakgFnwDYsKBAlux
Example Output: eTcakgFnwD

Example Input: FXBABLblGXBbPPTeauDTYol, nIVIEqtGdlGXBbPPTeYqlmcPrL
Example Output:
lGXBbPPTe