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

Example Input: oCtWZYdkvZ, pkktWZYdEHMW
Example Output: tWZYd

Example Input: yQRDycTycwH, ImycTycrR
Example Output: ycTyc

Example Input: bmZKWkYPqugcvzbHykblPzQLhK, tPUzKqugcvzbHypzk
Example Output:
qugcvzbHy