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

Example Input: xfZYYDKEqoRRu, ztCeYYDKEqoPG
Example Output: YYDKEqo

Example Input: gXwuhXJrEdzGOmLSKdK, TohXJrEdzGavU
Example Output: hXJrEdzG

Example Input: hkhmoIqgxMDNJavkvo, HBXRHpIqgxMDNJatYdwJSO
Example Output:
IqgxMDNJa