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

Example Input: rPPfxUdowLLdvwRtY, PuHovApkfxUdowLLBOhq
Example Output: fxUdowLL

Example Input: ZKMRTxCxbsbX, iovHrMRTxCxbsjv
Example Output: MRTxCxbs

Example Input: djCJjbXfJLYKBWhOrlqkLT, nOXfJLYKBWMeeNanu
Example Output:
XfJLYKBW