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

Example Input: OyXwTWbLByC, yODnTWbLWYzc
Example Output: TWbL

Example Input: zBNTHKtofMdHfBgJhOfojzM, VIkVdFapofMdHfBgjPCUo
Example Output: ofMdHfBg

Example Input: TQoQDVlVbnC, KRtzQDVlVHbMdx
Example Output:
QDVlV