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

Example Input: QvtDqzQiSknPbRCG, hVxHdqzQiSknPbumdpNIf
Example Output: qzQiSknPb

Example Input: MSzHyOuaJILkeY, eUibEHoHyOuaJIhfvXy
Example Output: HyOuaJI

Example Input: ylnvyUUghEvx, thFyUUghDDw
Example Output:
yUUgh