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

Example Input: WRfFDeZjIcpidmDxtaJcv, XMxWZjIcpidmlKga
Example Output: ZjIcpidm

Example Input: GFhJafTV, waHhJaji
Example Output: hJa

Example Input: vcKiBNQwO, xjdKiBNsQJy
Example Output:
KiBN

