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

Example Input: VRamNL, mUamIB
Example Output: am

Example Input: yQCDWefwvrPP, RwoMDWefwhSxTR
Example Output: DWefw

Example Input: yIfYJuV, BdhfYJHpK
Example Output:
fYJ