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

[EX Q]: UiaECWZf, gRyaECWLGRl
[EX A]: aECW

[EX Q]: tmBlKUto, eFDBlKLy
[EX A]: BlK

[EX Q]: IADZWzJO, lDzDZWbA
[EX A]:
DZW