instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
nXVXIEGP, fkXIEkU
answer:
XIE


question:
BrDGrTD, PBHDGrDw
answer:
DGr


question:
PQvmwldWGxucml, ApwwldWGeYM
answer:

wldWG