instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
nTAXUw, OWAXYU
answer:
AX


question:
yhhzISsXKEbA, KlPrazISsXKzmrVBG
answer:
zISsXK


question:
TNJTsGnbyKbSIb, urGnbyKiMW
answer:

GnbyK