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: FgQsxN, UMQsIa
Example Output: Qs

Example Input: ZnebMMFMiYwpMSXcUYyJABhjUD, jbZvQCNbEYwpMSXcUYDMbOoTSu
Example Output:
YwpMSXcUY

