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:
kyADtWLlnmYv, tcaKvDtWLlnvBq
answer:
DtWLln


question:
HlhHVrACUfJ, WbVrACUmS
answer:

VrACU