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

[EX Q]: gWMyioGBRpwcXfr, AOQGBRpwcSccqBE
[EX A]: GBRpwc

[EX Q]: wlFcxOHoXC, IWFcxOIWTk
[EX A]: FcxO

[EX Q]: kJtyNQQTLwdRvRD, zuVgCQQTLwIBZVW
[EX A]:
QQTLw