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

Example Input: zmbmQuyNGOe, mUMEmQuyiuS
Example Output: mQuy

Example Input: cxYVucnmEQopeWHrPJ, jNnOaYVucnmEQoSE
Example Output: YVucnmEQo

Example Input: NFYjtaKHRu, LFkbYjtaXic
Example Output:
Yjta