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

Example Input: EeUODjkxsQeTSNsHYpBKIUvEuAKhB, SrpZeTSNsHYpBKdhPFlgMh
Example Output: eTSNsHYpBK

Example Input: EJZYVxgFxPoOSDlLfK, uTLTIETHZYVxgFxPoPwr
Example Output: ZYVxgFxPo

Example Input: epGFYw, MVGFRI
Example Output:
GF