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

Example Input: libDFDxIgRiglWfxMVRr, yMltDxIgRiglpms
Example Output: DxIgRigl

Example Input: PQSFjlnU, kTSFjMUh
Example Output: SFj

Example Input: vZTTjlOZpn, TeNTjlOZRoL
Example Output:
TjlOZ