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

Example Input: zBNTHKtofMdHfBgJhOfojzM, VIkVdFapofMdHfBgjPCUo
Example Output: ofMdHfBg

Example Input: STvKOHq, XMGvKOdyM
Example Output: vKO

Example Input: SpEFsuXOORIJCAkfJqtBwtiYiRHXZ, zXiIJCAkfJqtBfQKRuOG
Example Output:
IJCAkfJqtB