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: jAinxmaQUrmu, jqeEnxmaQUrWlrEqW
Example Output: nxmaQUr

Example Input: FklmvJ, HZlmZz
Example Output:
lm