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

[EX Q]: SFQHJlK, dHfQHJoUC
[EX A]: QHJ

[EX Q]: dxqZUOvRprXyFfjQfTWBhR, biSVjOvRprXyFfDtuFWQ
[EX A]: OvRprXyFf

[EX Q]: MOKmFPFzJuCtCDvtPLNH, roSjzzzJuCtCDKPc
[EX A]:
zJuCtCD