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

Example Input: uZSRkFDHsGXNMaggxUn, lTrQKKpsGXNMaggEdSrEX
Example Output: sGXNMagg

Example Input: txJhzNeBj, qLJhzNesV
Example Output: JhzNe

Example Input: CxwZWv, mkwZgM
Example Output:
wZ