instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
NmtypJ, tQtyZD
answer:
ty


question:
yhhzISsXKEbA, KlPrazISsXKzmrVBG
answer:
zISsXK


question:
rYGiOTQAewQvFZ, oebFZobxXGiOTQAewQndCU
answer:

GiOTQAewQ