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

Ex Input:
kvutZfcPKzHE, kTKutZfcPTGmU

Ex Output:
utZfcP

Ex Input:
elloYaejTczBiiNOU, XoCPzloYaejTcXYtKODL

Ex Output:
loYaejTc

Ex Input:
ESzrxHnfaZ, XWrxHndj

Ex Output:
rxHn