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

Example Input: mvIvSzMtYsfVLdaGEmef, wnzMtYsfVLdaKm
Example Output: zMtYsfVLda

Example Input: zqRbqwgmqGIAGTeeoGFOSr, RFnLqwgmqGIAGLcEvAWxY
Example Output: qwgmqGIAG

Example Input: OcGzCq, HNGzoH
Example Output:
Gz