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

Example Input: GBTHKtWUzK, ovVNKtWUmVJF
Example Output: KtWU

Example Input: GnElFKBIoYmAdvz, GrElFKBIoMo
Example Output: ElFKBIo

Example Input: uxLqEHQnqrEOlayNBeDsPUBkvbp, wcilmzsmEOlayNBeDsNwAumxMH
Example Output:
EOlayNBeDs