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

Example Input: iYuUgULgqcAgd, kRNUgULgqFv
Example Output: UgULgq

Example Input: ftvxfhsnJEygzV, JYxSfhsnJnIqkW
Example Output: fhsnJ

Example Input: jauJftQgapTBiQgSoX, RNXtQgapTBikeIH
Example Output:
tQgapTBi