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

Example Input: sHndIbPaygfNvnquxIHeteW, huLmJWXZIgfNvnquxIViQDhbuoL
Example Output: gfNvnquxI

Example Input: EyvnjbVLF, vqnjblzR
Example Output: njb

Example Input: xqyUixxdbEgBBgxeT, pSUixxdbEPWcK
Example Output:
UixxdbE