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

Example Input: CdRbREFMEDTXnEzgn, zHLEMMEDTXnEPH
Example Output: MEDTXnE

Example Input: EJZYVxgFxPoOSDlLfK, uTLTIETHZYVxgFxPoPwr
Example Output: ZYVxgFxPo

Example Input: ygiCFem, vDiCFprz
Example Output:
iCF