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

Q: QvtDqzQiSknPbRCG, hVxHdqzQiSknPbumdpNIf

A: qzQiSknPb
****
Q: sbQJFbUtmnKaEJePFPeRM, QzfvkdZbUtmnKaEJNrWD

A: bUtmnKaEJ
****
Q: yvfbyG, zkfbaL

A:
fb
****