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

Example Input: fWJdaAfOCfejXZvidHM, gOpfOCfejXZbtLvSLZI
Example Output: fOCfejXZ

Example Input: ICizmXnKMpUH, oDrnmXnKgWXX
Example Output: mXnK

Example Input: TiZHJUrPzR, NoJUrPchun
Example Output:
JUrP