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: UmYbssMbmsXkKQuzNasLOib, EMqlbmsXkKQuzNcyHrpZXOQW
Example Output: bmsXkKQuzN

Example Input: PKvzaiCYUpDXgLdLtrWH, dmXzaiCYUpDXnZBjb
Example Output:
zaiCYUpDX