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

Example Input: QlJnxO, BLJnCQ
Example Output: Jn

Example Input: vhZuXCsIkQR, YflCuXCsIkLu
Example Output: uXCsIk

Example Input: NEUddFgmMHzPlpynb, YtfgdFgmMHzPIHOFlX
Example Output:
dFgmMHzP