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

Example Input: QvtDqzQiSknPbRCG, hVxHdqzQiSknPbumdpNIf
Example Output: qzQiSknPb

Example Input: jLbHvZmecfxMcGLXGVsO, erFBGmecfxMcJtDyKGZ
Example Output: mecfxMc

Example Input: DWnUJzLvOUtZFhZKcdpDkv, jcYPTzjuwvOUtZFhZKcFVXymomF
Example Output:
vOUtZFhZKc