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

Example Input: WjyKtxKtEYjP, vuBZJZyKtxKtXRZs
Example Output: yKtxKt

Example Input: zeuyZKwvIOfx, BlmZKwvspUt
Example Output: ZKwv

Example Input: tsQXNTqBMyctpdl, IDhNNTqBMyckbtD
Example Output:
NTqBMyc