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

Ex Input:
FSwxBJ, iTwxAa

Ex Output:
wx

Ex Input:
krnkpodgfpCKtfCqyzUbymWbxi, DydgSWpCKtfCqyzDaMsjqc

Ex Output:
pCKtfCqyz

Ex Input:
sEYtoQlG, XIstoQQPw

Ex Output:
toQ