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

Example Input: cvRdSsuNwGVEwSSrowDpaOu, gFMcLKIeLwNwGVEwSSroUGskaoloqC
Example Output: NwGVEwSSro

Example Input: mjCEUoPmeKbvCgUtUL, SrHtrPmeKbvYpQAVp
Example Output: PmeKbv

Example Input: tOvFuW, FivFFb
Example Output:
vF