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

Example Input: gfDDsblwUryUw, UWaRisblwUTqTM
Example Output: sblwU

Example Input: RGImMTISYdkjzMO, pmyfpImMTISYdatLBBFr
Example Output: ImMTISYd

Example Input: qDdOJxlVleahCiIhHSsEBdk, XjQFfaEKleahCiIhubQUCuTQ
Example Output:
leahCiIh