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

Example Input: cCDTMXjGMNikONun, jpcMXjGMNizBEWQzT
Example Output: MXjGMNi

Example Input: TnHJcxtwcZ, XFdHJcxNKw
Example Output: HJcx

Example Input: yUvMmCGaQOsuqF, pXvDvMmCGaiAHJA
Example Output:
vMmCGa