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

Example Input: bmZKWkYPqugcvzbHykblPzQLhK, tPUzKqugcvzbHypzk
Example Output: qugcvzbHy

Example Input: uZSRkFDHsGXNMaggxUn, lTrQKKpsGXNMaggEdSrEX
Example Output: sGXNMagg

Example Input: jATLwXKgDdlOwdO, QJXwXKgDdlOJeitzF
Example Output:
wXKgDdlO

