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

[EX Q]: ARGchkRez, kUwchkZPE
[EX A]: chk

[EX Q]: oHoJrr, YAoJSq
[EX A]: oJ

[EX Q]: NNpkdhvgT, BMkAkdhvrwV
[EX A]:
kdhv