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

[EX Q]: VLxrvK, gvxrac
[EX A]: xr

[EX Q]: XpFCxFOgTTNCnQzMnVPV, FMqzdOwgTTNCnQzedorxVPe
[EX A]: gTTNCnQz

[EX Q]: lAbOTmxfEViORT, GNMsWbOTmxfEViOpaR
[EX A]:
bOTmxfEViO