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

Example Input: oDdulHNcCdgbRGxiBTxM, kDcCdgbRGnsJlvas
Example Output: cCdgbRG

Example Input: DUhUbmfLuOFAQann, kwnzfLuOFAErR
Example Output: fLuOFA

Example Input: CgmFfBeLTOAeNmmei, gXGeLTOAeNQxe
Example Output:
eLTOAeN