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

Example Input: iaXeqfIrYKxPJRXxfSm, rIYKxPJRXxfsjVsqe
Example Output: YKxPJRXxf

Example Input: WRfFDeZjIcpidmDxtaJcv, XMxWZjIcpidmlKga
Example Output: ZjIcpidm

Example Input: NxUjlPWnW, WIjlPWYgky
Example Output:
jlPW