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

[EX Q]: UovaYpHjYSQzrfsxRfvIZE, pUOFxIKOGQzrfsxRfvIjrza
[EX A]: QzrfsxRfvI

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

[EX Q]: YVOkFt, zLOkcY
[EX A]:
Ok