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

[EX Q]: sGrHRmELarByxp, cDCUnmELarBXbEfM
[EX A]: mELarB

[EX Q]: sbQJFbUtmnKaEJePFPeRM, QzfvkdZbUtmnKaEJNrWD
[EX A]: bUtmnKaEJ

[EX Q]: Wnpfoo, Htpfjr
[EX A]:
pf