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

Example Input: gXwuhXJrEdzGOmLSKdK, TohXJrEdzGavU
Example Output: hXJrEdzG

Example Input: nFgMXUzpStDAybiwm, aNJrXUzpStDjp
Example Output: XUzpStD

Example Input: nfWdSHRttRifQwYVfn, fzVWdSHRttRMCbGaS
Example Output:
WdSHRttR