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

Example Input: cvZfWOwa, xOfWOhZs
Example Output: fWO

Example Input: gXwuhXJrEdzGOmLSKdK, TohXJrEdzGavU
Example Output: hXJrEdzG

Example Input: yGoxboWNA, iErxboNF
Example Output:
xbo