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

Example Input: IKrQfT, crrQRg
Example Output: rQ

Example Input: tftBHoDOYxCoTHVf, qhHoDOYxfUU
Example Output: HoDOYx

Example Input: kVIepSxMNnCBmwYGIc, sNnIepSxMNnCUaf
Example Output:
IepSxMNnC