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

Example Input: wCfNCfxvLRAxBstRTwMSqTn, AhwxfFNCfxvLRAxBrNtf
Example Output: NCfxvLRAxB

Example Input: fVEFJa, WtEFYK
Example Output: EF

Example Input: WPcyvqpCUcHwbM, OIBvqpCUcHwoRTI
Example Output:
vqpCUcHw