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

[EX Q]: GBTHKtWUzK, ovVNKtWUmVJF
[EX A]: KtWU

[EX Q]: bmZKWkYPqugcvzbHykblPzQLhK, tPUzKqugcvzbHypzk
[EX A]: qugcvzbHy

[EX Q]: elwtGi, pJwtnR
[EX A]:
wt