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

Example Input: CxosNa, ikosdx
Example Output: os

Example Input: yITbYie, TlqTbYomH
Example Output: TbY

Example Input: MfLieCNTtKopnbmqm, KGahVieCNTtKHDqVKnz
Example Output:
ieCNTtK