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

Ex Input:
cjDuPZOHjystHnF, okWVdUDuPZOHjSCaEecP

Ex Output:
DuPZOHj

Ex Input:
tyVlHfTPLRSdFilXnSfqQ, bkTPLRSdFiMgXC

Ex Output:
TPLRSdFi

Ex Input:
dyVcpkRIi, yhKcpkJSM

Ex Output:
cpk