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: koddLvYmRXDUuUnW, GnqDYGmmRXDUuUquAnf
Example Output: mRXDUuU

Example Input: UzJGAAvgJqDeVR, CuwvgJqDeqr
Example Output:
vgJqDe