In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
--------
Question: iYuUgULgqcAgd, kRNUgULgqFv

Answer: UgULgq


Question: lMRuEThD, wqQRuEKp

Answer: RuE


Question: duQRUMNMb, rEyRUMzK

Answer:
RUM